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Biology LibreTexts

Glossary

  • Page ID
    39895
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    (Eg. "Genetic, Hereditary, DNA ...") (Eg. "Relating to genes or heredity") The infamous double helix bio.libretexts.org/ CC-BY-SA; Delmar Larsen
    Glossary Entries

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    454 sequencing (pyrosequencing), 454 sequencing, pyrosequencing a next generation sequencing technique in which fragmented DNA has DNA adapters attached, is amplified by PCR, is attached to a bead, and then placed into a well with sequencing reagents, and the flash of light produced by the release of pyrophosphate on addition of a nucleotide is monitored        
    5’ cap methylguanosine nucleotide added to 5’ end of a eukaryotic primary transcript        
    70S ribosome a ribosome composed of 50S and 30S subunits        
    80S ribosome cytoplasmic eukaryotic ribosome composed of 60S and 40S subunits        
    α-helix secondary structure consisting of a helix stabilized by hydrogen bonds between nearby amino acid residues in a polypeptide        
    A (aminoacyl) site functional site of an intact ribosome that binds incoming charged aminoacyl tRNAs        
    A-B exotoxin class of exotoxin that contains A subunits, which enter the cell and disrupt cellular activities, and B subunits, which bind to host cell receptors        
    ABO blood group system set of glycoprotein antigens found on the surface of red blood cells; the presence or absence of specific carbohydrates determining blood type        
    absorbance when a molecule captures energy from a photon and vibrates or stretches, using the energy        
    Acanthamoeba keratitis a condition characterized by damage to the cornea and possible blindness caused by parasitic infection of the protozoan Acanthamoeba        
    acellular not made of cells        
    acid-fast stain a stain that differentiates cells that have waxy mycolic acids in their gram-positive cell walls        
    acidic dye a chromophore with a negative charge that attaches to positively charged structures        
    acidophile organism that grows optimally at a pH near 3.0        
    acne a skin disease in which hair follicles or pores become clogged, leading to the formation of comedones and infected lesions        
    acquired immunodeficiency syndrome (AIDS) disease caused by HIV, characterized by opportunistic infections and rare cancers        
    actin a protein that polymerizes to form microfilaments        
    activation energy energy needed to form or break chemical bonds and convert a reactant or reactants to a product or products        
    activator protein that increases the transcription of a gene in response to an external stimulus        
    active carrier an infected individual who can transmit the pathogen to others regardless of whether symptoms are currently present        
    active immunity stimulation of one’s own adaptive immune responses        
    active site location within an enzyme where substrate(s) bind        
    acute disease disease of a relatively short duration that develops and progresses in a predictable pattern        
    acute glomerulonephritis inflammation of the glomeruli of the kidney, probably resulting from deposition of immune complexes and an autoimmune response caused by self-antigen mimicry by a pathogen        
    acute necrotizing ulcerative gingivitis a severe form of gingivitis, also called trench mouth        
    acute otitis media inflammatory disease of the middle ear resulting from a microbial infection        
    acute rheumatic fever sequela of streptococcal pharyngitis; comorbidities include arthritis and carditis        
    acute-phase proteins antimicrobial molecules produced by liver cells in response to pathogen-induced stimulation events        
    acyclovir antiviral guanosine analog; inhibits DNA replication        
    adaptive immunity third-line defense characterized by specificity and memory        
    Addison disease autoimmune disease affecting adrenal gland function        
    adenine purine nitrogenous base found in nucleotides        
    adenosine diphosphate (ADP) nucleotide derivative and relative of ATP containing only one high-energy phosphate bond        
    adenosine monophosphate (AMP) adenine molecule bonded to a ribose molecule and to a single phosphate group, having no high-energy phosphate bonds        
    adenosine triphosphate (ATP) energy currency of the cell; a nucleotide derivative that safely stores chemical energy in its two high-energy phosphate bonds        
    adhesins molecules on the surface of pathogens that promote colonization of host tissue        
    adhesion the capability of microbes to attach to host cells        
    aerobic respiration use of an oxygen molecule as the final electron acceptor of the electron transport system        
    aerotolerant anaerobe organism that does not use oxygen but tolerates its presence        
    affinity maturation function of the immune system by which B cells, upon re-exposure to antigen, are selected to produce higher affinity antibodies        
    affinity measure of how tightly an antibody-binding site binds to its epitope        
    aflatoxin chemical produced by the fungus Aspergillus flavus; both a toxin and the most potent known natural carcinogen        
    African sleeping sickness see human African trypanosomiasis        
    agarose gel electrophoresis a method for separating populations of DNA molecules of varying sizes by differential migration rates caused by a voltage gradient through a horizontal gel matrix        
    agglutination binding of different pathogen cells by Fab regions of the same antibody to aggregate and enhance elimination from body        
    agranulocytes leukocytes that lack granules in the cytoplasm        
    alarmone small intracellular derivative of a nucleotide that signals a global bacterial response (i.e., activating a regulon of operons) to an environmental stress        
    albendazole antihelminthic drug of the benzimidazole class that binds to helminthic β-tubulin, preventing microtubule formation        
    algae (singular: alga) any of various unicellular and multicellular photosynthetic eukaryotic organisms; distinguished from plants by their lack of vascular tissues and organs        
    alkaliphile organism that grows optimally at pH above 9.0        
    alkylating agent type of strong disinfecting chemical that acts by replacing a hydrogen atom within a molecule with an alkyl group, thereby inactivating enzymes and nucleic acids        
    allergen antigen capable of inducing type I hypersensitivity reaction        
    allergy hypersensitivity response to an allergen        
    allograft transplanted tissue from an individual of the same species that is genetically different from the recipient        
    allosteric activator molecule that binds to an enzyme’s allosteric site, increasing the affinity of the enzyme’s active site for the substrate(s)        
    allosteric site location within an enzyme, other than the active site, to which molecules can bind, regulating enzyme activity        
    allylamines class of antifungal drugs that inhibit ergosterol biosynthesis at an early point in the pathway        
    Alphaproteobacteria class of Proteobacteria that are all oligotrophs        
    alveoli cul-de-sacs or small air pockets within the lung that facilitate gas exchange        
    amantadine antiviral drug that targets the influenza virus by preventing viral escape from endosomes upon host cell uptake, thus preventing viral RNA release and subsequent viral replication        
    amensalism type of symbiosis in which one population harms the other but remains unaffected itself        
    Ames test method that uses auxotrophic bacteria to detect mutations resulting from exposure to potentially mutagenic chemical compounds        
    amino acid a molecule consisting of a hydrogen atom, a carboxyl group, and an amine group bonded to the same carbon. The group bonded to the carbon varies and is represented by an R in the structural formula        
    aminoacyl-tRNA synthetase enzyme that binds to a tRNA molecule and catalyzes the addition of the correct amino acid to the tRNA        
    aminoglycosides protein synthesis inhibitors that bind to the 30S subunit and interfere with the ribosome’s proofreading ability, leading to the generation of faulty proteins that insert into and disrupt the bacterial cytoplasmic membrane        
    amoebiasis intestinal infection caused by Entamoeba histolytica        
    amoebic dysentery severe form of intestinal infection caused by Entamoeba histolytica, characterized by severe diarrhea with blood and mucus        
    amphipathic a molecule containing both polar and nonpolar parts        
    amphitrichous having two flagella or tufts of multiple flagella, with one flagellum or tuft located at each end of the bacterial cell        
    amphotericin B antifungal drug of the polyene class that is used to treat several systemic fungal infections        
    amplitude the height of a wave        
    anabolism chemical reactions that convert simpler molecules into more complex ones        
    anaerobe chamber closed compartment used to handle and grow obligate anaerobic cultures        
    anaerobe jar container devoid of oxygen used to grow obligate anaerobes        
    anaerobic respiration use of a non-oxygen inorganic molecule, like CO2, nitrate, nitrite, oxidized iron, or sulfate, as the final electron acceptor at the end of the electron transport system        
    analytical epidemiology study of disease outbreaks to establish associations between an agent and a disease state through observational studies comparing groups of individuals        
    anaphylactic shock another term for anaphylaxis        
    anaphylaxis systemic and potentially life-threatening type I hypersensitivity reaction        
    anergy peripheral tolerance mechanism that prevents self-reactive T cells from being activated by self-antigens through lack of co-stimulation        
    annealing formation of hydrogen bonds between the nucleotide base pairs of two single-stranded complementary nucleic acid sequences        
    anoxygenic photosynthesis type of photosynthesis found in many photosynthetic bacteria, including the purple and green bacteria, where an electron donor other than H2O is used to replace an electron lost by a reaction center pigment, resulting no oxygen production        
    anthrax a disease caused by Bacillus anthracis; the cutaneous form causes a skin lesion to develop; gastrointestinal and inhalation anthrax have high mortality rates        
    antibiogram compilation of the antimicrobial susceptibilities recorded for local bacterial strains, which is useful for monitoring local trends in antimicrobial resistance and aiding the prescription of appropriate empiric antibacterial therapy        
    antibiotic-associated diarrhea diarrhea that develops after antibiotic treatment as a result of disruption to the normal microbiota; C. difficile is a particularly serious example        
    antibody screen test to make sure that a potential blood recipient has not produced antibodies to antigens other than the ABO and Rh antigens        
    antibody Y-shaped glycoprotein molecule produced by B cells that binds to specific epitopes on an antigen        
    antibody-dependent cell-mediated cytotoxicity (ADCC) mechanism by which large pathogens are marked for destruction by specific antibodies and then killed by secretion of cytotoxins by natural killer cells, macrophages, or eosinophils        
    anticodon three-nucleotide sequence of a mature tRNA that interacts with an mRNA codon through complementary base pairing        
    antigen, immunogen a molecule that stimulates an adaptive immune response        
    antigenic able to stimulate an adaptive immune response        
    antigenic drift form of slight antigenic variation that occurs because of point mutations in the genes that encode surface proteins        
    antigenic shift form of major antigenic variation that occurs because of gene reassortment        
    antigenic variation changing of surface antigens (carbohydrates or proteins) such that they are no longer recognized by the host’s immune system        
    antigen-presenting cells (APC) macrophages, dendritic cells, and B cells that process and present foreign pathogen antigens for the purpose of activating T cells and adaptive immune defenses        
    antimetabolites compounds that are competitive inhibitors for bacterial metabolic enzymes        
    antimicrobial drugs chemical compounds, including naturally produced drugs, semisynthetic derivatives, and synthetic compounds, that target specific microbial structures and enzymes, killing specific microbes or inhibiting their growth        
    antimicrobial peptides (AMPs) class of nonspecific, cell-derived chemical mediators with broad-spectrum antimicrobial properties        
    antiparallel two strands of DNA helix oriented in opposite directions; one strand is oriented in the 5’ to 3’ direction, while the other is oriented in the 3’ to 5’ direction        
    antisense RNA small noncoding RNA molecules that inhibit gene expression by binding to mRNA transcripts via complementary base pairing        
    antisense strand transcription template strand of DNA; the strand that is transcribed for gene expression        
    antisepsis protocol that removes potential pathogens from living tissue        
    antiseptic antimicrobial chemical that can be used safely on living tissue        
    antiserum serum obtained from an animal containing antibodies against a particular antigen that was artificially introduced to the animal        
    apoenzyme enzyme without its cofactor or coenzyme        
    apoptosis programmed and organized cell death without lysis of the cell        
    arachnoid mater middle membrane surrounding the brain that produces cerebrospinal fluid        
    arboviral encephalitis infection by an arthropod-borne virus that results in an inflammation of the brain        
    arbovirus any of a variety of viruses that are transmitted by arthropod vectors        
    archaea any of various unicellular prokaryotic microorganisms, typically having cell walls containing pseudopeptidoglycan        
    Archaea domain of life separate from the domains Bacteria and Eukarya        
    artemisinin antiprotozoan and antifungal drug effective against malaria that is thought to increase intracellular levels of reactive oxygen species in target microbes        
    artery large, thick-walled vessel that carries blood from the heart to the body tissues        
    Arthus reaction localized type III hypersensitivity        
    artificial active immunity immunity acquired through exposure to pathogens and pathogen antigens through a method other than natural infection        
    artificial passive immunity transfer of antibodies produced by a donor to another individual for the purpose of preventing or treating disease        
    ascariasis soil-transmitted intestinal infection caused by the large nematode roundworm Ascaris lumbricoides        
    ascocarps cup-shaped fruiting bodies of an ascomycete fungus        
    ascospore asexual spore produced by ascomycete fungi        
    ascus structure of ascomycete fungi containing spores        
    asepsis sterile state resulting from proper use of microbial control protocols        
    aseptic technique method or protocol designed to prevent microbial contamination of sterile objects, locations, or tissues        
    aspergillosis fungal infection caused by the mold Aspergillus; immunocompromised patients are primarily at risk        
    asymptomatic carrier an infected individual who exhibits no signs or symptoms of disease yet is capable of transmitting the pathogen to others        
    asymptomatic not exhibiting any symptoms of disease        
    atomic force microscope a scanning probe microscope that uses a thin probe that is passed just above the specimen to measure forces between the atoms and the probe        
    ATP synthase integral membrane protein that harnesses the energy of the proton motive force by allowing hydrogen ions to diffuse down their electrochemical gradient, causing components of this protein to spin, making ATP from ADP and Pi        
    attachment binding of phage or virus to host cell receptors        
    attenuation regulatory system of prokaryotes whereby secondary stem-loop structures formed within the 5’ end of an mRNA being transcribed determine both if transcription to complete the synthesis of this mRNA will occur and if this mRNA will be used for translation        
    autoclave specialized device for the moist-heat sterilization of materials through the application of pressure to steam, allowing the steam to reach temperatures above the boiling point of water        
    autocrine function refers to a cytokine signal released from a cell to a receptor on its own surface        
    autograft tissue transplanted from a location on an individual to a different location on the same individual        
    autoimmune disease loss of tolerance to self, resulting in immune-mediated destruction of self cells and tissues        
    autoinducer signaling molecule produced by a bacterial cell that can modify the activity of surrounding cells; associated with quorum sensing        
    autoradiography the method of producing a photographic image from radioactive decay; in molecular genetics the method allows the visualization of radioactively-labeled DNA probes that have hybridized to a nucleic acid sample        
    autotroph, autotrophs organism that converts inorganic carbon dioxide into organic carbon        
    auxotroph, auxotrophs nutritional mutant with a loss-of-function mutation in a gene encoding the biosynthesis of a specific nutrient such as an amino acid        
    avidity strength of the sum of the interactions between an antibody and antigen        
    axon long projection of a neuron along which an electrochemical signal is transmitted        
    azithromycin semisynthetic macrolide with increased spectrum of activity, decreased toxicity, and increased half-life compared with erythromycin        
    β-lactamases bacterially produced enzymes that cleave the β-lactam ring of susceptible β-lactam antimicrobials, rendering them inactive and conferring resistance        
    β-lactams group of antimicrobials that inhibit cell wall synthesis; includes the penicillins, cephalosporins, carbapenems, and monobactams; inhibits the transpeptidase cross-linking activity of penicillin-binding proteins        
    β-oxidation process of fatty acid degradation that sequentially removes two-carbon acetyl groups, producing NADH and FADH2, on entry into the Krebs cycle        
    β-pleated sheet secondary structure consisting of pleats formed by hydrogen bonds between localized segments of amino acid residues on the backbone of the polypeptide chain        
    B-cell receptors (BCRs) membrane-bound IgD and IgM antibody that bind specific antigen epitopes with Fab antigen-binding region        
    B lymphocyte antibody-producing cells of humoral immunity; B cell        
    babesiosis tickborne protozoan infection caused by Babesia spp. and characterized by malaise, fatigue, fever, headache, myalgia, and joint pain        
    bacillary dysentery gastrointestinal illness caused by Shigella bacteria, also called shigellosis        
    bacillus (bacilli) rod-shaped prokaryotic cell        
    bacitracin group of structurally similar peptides that block the movement of peptidoglycan precursors across the cell membrane, inhibiting peptidoglycan synthesis        
    bacteremia condition marked by the presence of bacteria in the blood        
    bacteria (singular: bacterium) any of various unicellular prokaryotic microorganisms typically (but not always) having cell wells that contain peptidoglycan        
    bacterial lawn layer of confluent bacterial growth on an agar plate        
    bacterial meningitis bacterial infection that results in an inflammation of the meninges        
    bacterial vaginosis a condition caused by an overgrowth of bacteria in the vagina that may or may not cause symptoms        
    bactericidal irreversible inhibition of a microbe’s ability to divide        
    bactericide chemical or physical treatment that kills bacteria        
    bacteriochlorophylls green, purple, or blue pigments of bacteria; they are similar to chlorophyll of plants        
    bacteriology the study of bacteria        
    bacteriophage, bacteriophages virus that infects bacteria        
    bacteriostatic having the ability to inhibit bacterial growth, generally by means of chemical or physical treatment; reversible inhibition of a microbe’s ability to divide        
    barophile organism that grows under high atmospheric pressure        
    basal body component of eukaryotic flagellum or cilium composed of nine microtubule triplets and attaches the flagellum or cilium to the cell        
    base sequence identity of the specific nucleotides present in a nucleic acid strand and their order within the strand        
    basic dye a chromophore with a positive charge that attaches to negatively charged structures        
    basidia, basidium small club-shaped structures of basidiomycete fungi where basidiospores are produced        
    basidiocarps fruiting bodies of basidiomycete fungi        
    basidiospores spores produced sexually via budding in basidiomycete fungi        
    basophils leukocytes with granules containing histamine and other chemicals that facilitate allergic responses and inflammation when released        
    benzimidazoles class of antihelminthic drugs that bind to helminthic β-tubulin, preventing microtubule formation        
    Betaproteobacteria class of Proteobacteria that are all eutrophs        
    binary fission predominant form of bacterial reproduction in which one cell divides into two daughter cells of equal size, which separate, each offspring receiving a complete copy of the parental genome        
    binocular having two eyepieces        
    binomial nomenclature a universal convention for the scientific naming of organisms using Latinized names for genus and species        
    biofilm complex ecosystem of bacteria embedded in a matrix        
    biogeochemical cycle recycling of inorganic matter between living organisms and their nonliving environment        
    bioinformatics the analysis of large amounts of information required for interpretation of these data        
    biological transmission movement of a pathogen between hosts facilitated by a biological vector in which the pathogen grows and reproduces        
    biological vector an animal (typically an arthropod) that is infected with a pathogen and is capable of transmitting the pathogen from one host to another        
    biomarker a protein expressed by a cell or tissue that is indicative of disease        
    biomolecule a molecule that is part of living matter        
    bioremediation use of microbes to remove xenobiotics or environmental pollutants from a contaminated site        
    biosynthesis replication of viral genome and other protein components        
    biotechnology the science of using living systems to benefit humankind        
    bisbiguanide type of chemical compound with antiseptic properties; disrupts cell membranes at low concentrations and causes congealing of intracellular contents at high concentrations        
    blastomycosis fungal disease associated with infections by Blastomyces dermatitidis; can cause disfiguring scarring of the hands and other extremities        
    blepharitis inflammation of the eyelids        
    blocking antibodies antigen-specific antibodies (usually of the IgG type) produced via desensitization therapy        
    blood-brain barrier tight cell junctions of the endothelia lining the blood vessels that serve the central nervous system, preventing passage of microbes from the bloodstream into the brain and cerebrospinal fluid        
    blue-white screening a technique commonly used for identifying transformed bacterial cells containing recombinant plasmids using lacZ-encoding plasmid vectors        
    blunt ends ends of DNA molecules lacking single-stranded complementary overhangs that are produced when some restriction enzymes cut DNA        
    botulism form of flaccid paraylsis caused by the ingestion of a neurotoxin produced by Clostridium botulinum        
    bradykinin activated form of a proinflammatory molecule induced in the presence of invader microbes; opens gaps between cells in blood vessels, allowing fluid and cells to leak into surrounding tissue        
    bridge reaction reaction linking glycolysis to the Krebs cycle during which each pyruvate is decarboxylated and oxidized (forming NADH), and the resulting two-carbon acetyl group is attached to a large carrier called coenzyme A, resulting in the formation of acetyl-CoA and CO; also called the transition reaction        
    brightfield microscope a compound light microscope with two lenses; it produces a dark image on a bright background        
    broad-spectrum antimicrobial drug that targets many different types of microbes        
    bronchi major air passages leading to the lungs after bifurcating at the windpipe        
    bronchioles smaller air passages within the lung that are formed as the bronchi become further subdivided        
    bronchitis inflammation of the bronchi        
    brucellosis zoonotic disease caused by bacteria of the genus Brucella that results in undulant fever        
    bubo swollen, inflamed lymph node that forms as a result of a microbial infection        
    bubonic plague most common form of plague in humans, marked by the presence of swollen lymph nodes (buboes)        
    budding unequal reproductive division in which a smaller cell detaches from the parent cell        
    budding yeasts yeasts that divide by budding off of daughter cells        
    Burkitt lymphoma disease characterized by rapidly growing solid tumor; caused by Epstein-Barr virus (HHV-4)        
    burst release of new virions by a lysed host cell infected by a virus        
    burst size the number of virions released from a host cell when it is lysed because of a viral infection        
    Calvin-Benson cycle  most common CO2 fixation pathway in most photoautotrophs; involves light-independent reactions of photosynthesis that occur in the cytoplasm of photosynthetic bacteria and in the stroma of eukaryotic chloroplasts        
    Campylobacter jejuni gastroenteritis  gastroenteritis caused by C. jejuni; generally mild but sometimes with serious complications        
    candidiasis  fungal infection caused by Candida spp., especially C. albicans; can affect various regions of the body, e.g., skin (cutaneous candidiasis), oral cavity (oral thrush), or vagina (yeast infection)        
    candle jar  container with a tight-fitting lid in which a burning candle consumes oxygen and releases carbon dioxide, thereby creating an environment suitable for capnophiles        
    capillary  small blood vessel found in the interstitial space of tissue; delivers nutrients and oxygen, and removes waste products        
    capnophile  organism that requires carbon dioxide levels higher than atmospheric concentration        
    capsid  protein coat surrounding the genome of the virus        
    capsomere  individual protein subunits that make up the capsid        
    capsule staining  a negative staining technique that stains around a bacterial capsule while leaving the capsule clear        
    capsule  type of glycocalyx with organized layers of polysaccharides that aid in bacterial adherence to surfaces and in evading destruction by immune cells        
    carbapenem-resistant Enterobacteriaceae (CRE)  group of bacteria that have developed resistance to all β-lactams, including carbapenems, and many other drug classes        
    carbohydrate  the most abundant type of biomolecule, consisting of carbon, hydrogen, and oxygen        
    carbon skeleton  chain of carbon atoms to which one or more functional groups are bound        
    carboxysome  an inclusion composed of an outer shell of thousands of protein subunits. Its interior is filled with ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) and carbonic anhydrase, which are both used for carbon metabolism        
    carbuncle  abscess containing a large, deep, purulent skin lesion        
    carcinogen, carcinogens  agent that causes cancer        
    case-control study  a type of observational study in which a group of affected individuals are compared, usually retrospectively, to a similar group of unaffected individuals        
    catabolic activator protein (CAP)/cAMP receptor protein (CRP)  protein that, when bound to cAMP in the presence of low levels of glucose, binds to the promoters of operons that control the processing of alternative sugars        
    catabolism  chemical reactions that break down complex molecules into simpler ones        
    catabolite repression  repression of the transcription of operons encoding enzymes for the use of substrates other than glucose when glucose levels are high        
    catalase  enzyme that breaks down hydrogen peroxide to water and oxygen        
    catalyst, catalysts  molecule that increases the rate of a chemical reaction but is not used or changed during the chemical reaction and, thus, is reusable        
    catarrhal stage  in pertussis, a disease stage marked by inflammation of the mucous membranes combined with excessive secretions        
    cat-scratch disease  bacterial infection of the lymph nodes caused by Bartonella henselae; frequently transmitted via a cat scratch        
    causative agent  the pathogen or substance responsible for causing a particular disease; etiologic agent        
    CCA amino acid binding end  region of a mature tRNA that binds to an amino acid        
    celiac disease  disease largely of the small intestine caused by an immune response to gluten that results in the production of autoantibodies and an inflammatory response        
    cell envelope  the combination of external cellular structures (e.g., plasma membrane, cell wall, outer membrane, glycocalyces) that collectively contain the cytoplasm and internal structures of a cell        
    cell membrane  lipid bilayer with embedded proteins and carbohydrates that defines the boundary of the cell (also called the cytoplasmic membrane or plasma membrane)        
    cell morphology  cell shape, structure, and arrangement, as viewed microscopically        
    cell theory  the theory that all organisms are composed of cells and that the cell is the fundamental unit of life        
    cell wall  a structure in the cell envelope of some cells that helps the cell maintain its shape and withstand changes in osmotic pressure        
    cellular immunity  adaptive immunity involving T cells and the destruction of pathogens and infected cells        
    cellulitis  a subcutaneous skin infection that develops in the dermis or hypodermis, resulting in a red, painful inflammation        
    cellulose  a structural polysaccharide composed of glucose monomers linked together in a linear chain by glycosidic bonds        
    Centers for Disease Control and Prevention (CDC)  the national public health agency in the United States        
    central dogma  scientific principle explaining the flow of genetic information from DNA to RNA to protein        
    central nervous system (CNS)  portion of the nervous system made up of the brain and spinal cord        
    central tolerance  negative selection of self-reactive T cells in thymus        
    centriole  a component of a centrosome with the structural array of nine parallel microtubules arranged in triplets; involved in eukaryotic cell division        
    centrosome  a microtubule-organizing center for the mitotic spindle found in animal cells; it separates chromosomes during cell division and is composed of a pair of centrioles positioned at right angles to each other        
    cephalosporins  a group of cell wall synthesis inhibitors within the class of β-lactams        
    cercarial dermatitis  inflammation of the skin caused by a reaction to cercaria of Schistosoma spp., which can penetrate the skin and blood vessels; also called swimmer’s itch or clam digger’s itch        
    cerebrospinal fluid (CSF)  sterile liquid produced in the brain that fills the subarachnoid space of the brain and spinal column        
    cervix  the part of the uterus that connects to the vagina        
    CFB group  phylum consisting of the gram-negative, rod-shaped nonproteobacteria genera CytophagaFusobacterium, and Bacteroides        
    Chagas disease  potentially fatal protozoan infection caused by Trypanosoma cruzi and endemic to Central and South America; transmitted by the triatomine bug (kissing bug)        
    chancroid  an STI caused by Haemophilus ducreyi that produces soft chancres on genitals        
    charged tRNA  activated tRNA molecule carrying its cognate amino acid        
    chemical mediators  chemicals or enzymes produced by a variety of cells; provide nonspecific antimicrobial defense mechanisms        
    chemically defined media  media in which all components are chemically defined        
    chemiosmosis  flow of hydrogen ions across the membrane through ATP synthase        
    chemokines  chemotactic cytokines that recruit specific subsets of leukocytes to infections, damaged tissue, and sites of inflammation        
    chemotaxis  directional movement of a cell in response to a chemical attractant        
    chemotroph, chemotrophs  organism that gets its energy from the transfer of electrons originating from chemical compounds        
    chickenpox  common childhood disease caused by the varicella-zoster virus and marked by the formation of pustular lesions on the trunk        
    chikungunya fever  mosquito-borne viral disease caused by the chikungunya virus and characterized by high fever, joint pain, rash, and blisters        
    chirality  property of stereoisomer molecules by which their structures are nonsuperimposable mirror-images        
    chitin  polysaccharide that is an important component of fungal cell walls        
    chlamydia  a common STI caused by Chlamydia trachomatis        
    chloramphenicol  protein synthesis inhibitor with broad-spectrum activity that binds to the 50S subunit, inhibiting peptide bond formation        
    chlorophyll  a type of photosynthetic pigment found in some prokaryotic and eukaryotic cells        
    chloroplast  organelle found in plant and algal cells in which photosynthesis occurs        
    cholera  gastrointestinal illness caused by Vibrio cholera characterized by severe diarrhea        
    chromatin  combination of DNA with DNA binding proteins        
    chromogenic substrate  colorless substrate (chromogen) that is converted into a colored end product by the enzyme        
    chromophores  pigments that absorb and reflect particular wavelengths of light (giving them a color)        
    chromosome  discrete DNA structure within a cell that controls cellular activities        
    chronic disease  any disease that progresses and persists over a long time        
    chronic granulomatous disease  primary immunodeficiency caused by an impaired ability of phagocytic cells to kill ingested bacteria in the phagolysosome        
    chronic wasting disease  prion disease of deer and elk in the United States and Canada        
    cilia (singular: cilium)  short filamentous structures found on some eukaryotic cells; each is composed of microtubules in a 9+2 array, and may be used for locomotion, feeding, and/or movement of extracellular particles that come in contact with the cell        
    ciliated epithelial cells  hair-like cells in the respiratory tract that beat, pushing mucus secretions and trapped debris away from the sensitive tissues of the lungs        
    ciliates  protists with cilia (Ciliophora), including Paramecium and Stentor, classified within the Chromalveolata        
    cisternae  the sacs of the endoplasmic reticulum        
    citric acid cycle  see Krebs cycle        
    class switching  genetic rearrangement of constant region gene segments in plasma cells to switch antibody production from IgM to IgG, IgA, or IgE        
    clindamycin  semisynthetic protein synthesis inhibitor of the lincosamide class that binds to the 50S subunit, inhibiting peptide bond formation        
    clone  a genetically identical cell or individual        
    Clostridium perfringens gastroenteritis  relatively mild gastrointestinal illness caused by C. perfringens        
    clusters of differentiation (CD)  cell-surface glycoproteins that serve to identify and distinguish white blood cells        
    coagulase  enzyme that causes the activation of fibrinogen to form fibrin, promoting clotting of the blood        
    coarse focusing knob  a knob on a microscope that produces relatively large movements to adjust focus        
    coccidioidomycosis  disease caused by the highly infectious fungal pathogen Coccidioides immitis and related species        
    codon  three-nucleotide sequence within mRNA that specifies a particular amino acid to be incorporated into the polypeptide being synthesized        
    coenocyte  multinucleated eukaryotic cell that forms as a result of multiple rounds of nuclear division without the accompanying division of the plasma membrane        
    coenocytic hyphae  nonseptate hyphae that are multinucleate and lack cell walls or membranes between cells; characteristic of some fungi        
    coenzyme  organic molecule required for proper enzyme function that is not consumed and is reusable        
    cofactor, cofactors  inorganic ion that helps stabilize enzyme conformation and function        
    cognate amino acid  amino acid added to a specific tRNA molecule that correctly corresponds to the tRNA’s anticodon and, hence, the mRNA’s codon, reflecting the genetic code        
    cohort method  a method used in observational studies in which a group of individuals is followed over time and factors potentially important in the development of disease are evaluated        
    colistin  membrane-active polymyxin that was historically used for bowel decontamination but now used for systemic infections with drug-resistant pathogens        
    colitis  inflammation of the large intestine        
    collagenase  enzyme that digests collagen, the dominant protein in connective tissue        
    colony-forming unit (CFU)  a counting quantity represented by a colony formed on solid medium from a single cell or a few cells        
    commensalism  type of symbiosis in which one population benefits and the other is not affected        
    commercial sterilization  type of sterilization protocol used in food production; uses conditions that are less harsh (lower temperatures) to preserve food quality but still effectively destroy vegetative cells and endospores of common foodborne pathogens such as Clostridium botulinum        
    common cold  most common cause of rhinitis in humans; associated with a variety of adenoviruses, coronaviruses, and rhinoviruses        
    common source spread  a mode of disease transmission in which every infection originates from the same source        
    communicable  able to be transmitted directly or indirectly from one person to another        
    community  group of interacting populations of organisms        
    competitive inhibitor  molecule that binds to an enzyme’s active site, preventing substrate binding        
    competitive interactions  interactions between populations in which one of them competes with another for resources        
    complement activation  cascading activation of the complement proteins in the blood, resulting in opsonization, inflammation, and lysis of pathogens        
    complement fixation test  test for antibodies against a specific pathogen using complement-mediated hemolysis        
    complement system  series of proteins that can become activated in the presence of invading microbes, resulting in opsonization, inflammation, and lysis of pathogens        
    complementary base pairs  base pairing due to hydrogen bonding that occurs between a specific purine and a specific pyrimidine; A bonds with T (in DNA), and C bonds with G        
    complementary DNA (cDNA)  a DNA molecule complementary to mRNA that is made through the activity of reverse transcriptase        
    complex media  media that contain extracts of animals and plants that are not chemically defined        
    complex virus  virus shape that often includes intricate characteristics not seen in the other categories of capsid        
    compound microscope  a microscope that uses multiple lenses to focus light from the specimen        
    condenser lens  a lens on a microscope that focuses light from the light source onto the specimen        
    conditional mutation  mutant form of a gene whose mutant phenotype is expressed only under certain environmental conditions        
    confocal microscope  a scanning laser microscope that uses fluorescent dyes and excitation lasers to create three-dimensional images        
    conidia  asexual fungal spores not enclosed in a sac; produced in a chain at the end of specialized hyphae called conidiophores        
    conjugate vaccine  a vaccine consisting of a polysaccharide antigen conjugated to a protein to enhance immune response to the polysaccharide; conjugate vaccines are important for young children who do not respond well to polysaccharide antigens        
    conjugated protein  protein carrying a nonpolypeptidic portion        
    conjugation  mechanism of horizontal gene transfer in bacteria in which DNA is directly transferred from one bacterial cell to another by a conjugation pilus        
    conjugation pilus (sex pilus)  hollow tube composed of protein encoded by the conjugation plasmid that brings two bacterial cells into contact with each other for the process of conjugation        
    conjunctiva  the mucous membranes covering the eyeball and inner eyelid        
    conjunctivitis  inflammation of the conjunctiva, the mucous membrane covering the eye and inside of the eyelid        
    constitutively expressed  describes genes that are transcribed and translated continuously to provide the cell with constant intermediate levels of the protein products        
    contact dermatitis  inflammation of the skin resulting from a type IV hypersensitivity to an allergen or irritant        
    contact  see exposure        
    contact transmission  movement of a pathogen between hosts due to contact between the two; may be direct or indirect        
    contagious  easily spread from person to person        
    continuous cell line  derived from transformed cells or tumors, these cells are often able to be subcultured many times, or, in the case of immortal cell lines, grown indefinitely        
    continuous common source spread  a mode of disease transmission in which every infection originates from the same source and that source produces infections for longer than one incubation period        
    contractile vacuoles  organelles found in some cells, especially in some protists, that take up water and then move the water out of the cell for osmoregulatory purposes (i.e., to maintain an appropriate salt and water balance)        
    contrast  visible differences between parts of a microscopic specimen        
    convalescence stage  the final stage of a whooping cough infection, marked by a chronic cough        
    Coombs’ reagent  antiserum containing antihuman immunoglobulins used to facilitate hemagglutination by cross-linking the human antibodies attached to red blood cells        
    cooperative interactions  interactions between populations in which both benefit        
    cortex  tightly packed layer of fungal filaments at the outer surface of a lichen; foliose lichens have a second cortex layer beneath the medulla        
    counterstain  a secondary stain that adds contrasting color to cells from which the primary stain has been washed out by a decolorizing agent        
    crenation  shriveling of a cell        
    Creutzfeldt-Jakob disease  form of transmissible spongiform encephalopathy found in humans; typically a fatal disease        
    crisis phase  point at which a fever breaks, reaching a peak before the hypothalamus resets back to normal body temperature        
    critical item  object that must be sterile because it will be used inside the body, often penetrating sterile tissues or the bloodstream        
    cross-match  in the major cross-match, donor red blood cells are checked for agglutination using recipient serum; in the minor cross-match, donor serum is checked for agglutinizing antibodies against recipient red blood cells        
    cross-presentation  a mechanism by which dendritic cells process antigens for MHC I presentation to CD8 T cells through phagocytosis of the pathogen (which would normally lead to MHC II presentation)        
    cross-resistance  when a single resistance mechanism confers resistance to multiple antimicrobial drugs        
    cross-sectional study  a type of observational study in which measurements are made on cases, both affected and unaffected, at one point in time and the measurements analyzed to uncover associations with the disease state        
    crustose lichens  lichens that are tightly attached to the substrate, giving them a crusty appearance        
    cryptococcosis  fungal pneumonia caused by the encapsulated yeast Cryptococcus neoformans commonly found in bird droppings        
    cryptosporidiosis  intestinal infection caused by Cryptosporidium parvum or C. hominis        
    culture density  the number of cells per volume of broth        
    culture medium  combination of compounds in solution that supports growth        
    cutaneous mycosis  any fungal infection that affects the surface of the skin, hair, or nails        
    cyanobacteria  phototrophic, chlorophyll-containing bacteria that produce large amounts of gaseous oxygen        
    cyclic AMP (cAMP)  intracellular signaling molecule made through the action of adenylyl cyclase from ATP when glucose levels are low, with the ability to bind to a catabolite activator protein to allow it to bind to regulatory regions and activate the transcription of operons encoding enzymes for metabolism of alternative substrates        
    cyclic photophosphorylation  pathway used in photosynthetic organisms when the cell’s need for ATP outweighs that for NADPH, thus bypassing NADPH production        
    cyclosporiasis  intestinal infection caused by Cyclospora cayetanensis        
    cystic echinococcosis  hydatid disease, an infection caused by the tapeworm Echinococcus granulosus that can cause cyst formation        
    cysticerci  larval form of a tapeworm        
    cystitis  inflammation of the bladder        
    cysts  microbial cells surrounded by a protective outer covering; some microbial cysts are formed to help the microbe survive harsh conditions, whereas others are a normal part of the life cycle        
    cytochrome oxidase  final ETS complex used in aerobic respiration that transfers energy-depleted electrons to oxygen to form H2O        
    cytokine storm  an excessive release of cytokines, typically triggered by a superantigen, that results in unregulated activation of T cells        
    cytokines  protein molecules that act as a chemical signals; produced by cells in response to a stimulation event        
    cytokinesis division of the cytoplasm following mitosis that forms two daughter cells        
    cytomegalovirus (CMV) infection  human herpesvirus 5 infection that is typically asymptomatic but can become serious in immunocompromised patients, transplant recipients, and developing fetuses        
    cytopathic effect, cytopathic effects  cell abnormality resulting from a viral infection        
    cytoplasm  the gel-like material composed of water and dissolved or suspended chemicals contained within the plasma membrane of a cell        
    cytoplasmic membrane  see cell membrane        
    cytoproct  a protozoan cell structure that is specialized for excretion        
    cytosine  pyrimidine nitrogenous base found in nucleotides        
    cytoskeleton  a network of filaments or tubules in the eukaryotic cell that provides shape and structural support for cells; aids movement of materials throughout the cell        
    cytostome  a protozoan cell structure that is specialized for phagocytosis (i.e., to take in food)        
    cytotoxic T cells  effector cells of cellular immunity that target and eliminate cells infected with intracellular pathogens through induction of apoptosis        
    cytotoxicity  harmful effects to host cell        
    dacryocystitis  inflammation of the lacrimal sac often associated with a plugged nasolacrimal duct        
    daptomycin  cyclic lipopetide that disrupts the bacterial cell membrane        
    darkfield microscope  a compound light microscope that produces a bright image on a dark background; typically a modified brightfield microscope        
    death phase (decline phase)  phase of the growth curve at which the number of dying cells exceeds the number of new cells formed        
    decimal reduction time (DRT) or D-value, decimal reduction time, D-value  amount of time it takes for a specific protocol to produce a one order of magnitude decrease in the number of organisms; that is, death of 90% of the population        
    decolorizing agent  a substance that removes a stain, usually from some parts of the specimen        
    deeply branching bacteria  bacteria that occupy the lowest branches of the phylogenetic tree of life        
    definitive host  the preferred host organism for a parasite, in which the parasite reaches maturity and may reproduce sexually        
    degeneracy  redundancy in the genetic code because a given amino acid is encoded by more than one nucleotide triplet codon        
    degerming  protocol that significantly reduces microbial numbers by using mild chemicals (e.g., soap) and gentle scrubbing of a small area of skin or tissue to avoid the transmission of pathogenic microbes        
    degranulation  release of the contents of mast cell granules in response to the cross-linking of IgE molecules on the cell surface with allergen molecules        
    dehydration synthesis  chemical reaction in which monomer molecules bind end to end in a process that results in the formation of water molecules as a byproduct        
    deletion  type of mutation involving the removal of one or more bases from a DNA sequence        
    Deltaproteobacteria  class of Proteobacteria that includes sulfate-reducing bacteria        
    denatured protein  protein that has lost its secondary and tertiary structures (and quaternary structure, if applicable) without the loss of its primary structure        
    dendrites  branched extensions of the soma of a neuron that interact with other cells        
    dengue fever  mosquito-borne viral hemorrhagic disease; also known as breakbone fever        
    dental calculus  calcified heavy plaque on teeth, also called tartar        
    dental caries  cavities formed in the teeth as a result of tooth decay caused by microbial activity        
    deoxyribonucleic acid (DNA), DNA  double-stranded nucleic acid composed of deoxyribonucleotides that serves as the genetic material of the cell        
    deoxyribonucleotides  DNA nucleotides containing deoxyribose as the pentose sugar component        
    dermatophyte  any fungus of the genera Microsporum, Epidermophyton, or Trichophyton, which feed on keratin (a protein found in skin, hair, and nails) and can cause cutaneous infections        
    dermis  the second layer of human skin, found between the epidermis and the hypodermis        
    descriptive epidemiology  a method of studying a disease outbreak using case histories, contact interviews, medical information, and other sources of information        
    desensitization  injections of antigen that lead to production of antigen-specific IgG molecules, effectively outcompeting IgE molecules on the surface of sensitized mast cells for antigen        
    desiccation  method of microbial control involving the removal of water from cells through drying or dehydration        
    desquamation  peeling and shedding of outermost skin        
    diapedesis  process by which leukocytes pass through capillary walls to reach infected tissue; also called extravasation        
    diaphragm  a component of a microscope; typically consists of a disk under the stage with holes of various sizes; can be adjusted to allow more or less light from the light source to reach the specimen        
    differential interference-contrast microscope  a microscope that uses polarized light to increase contrast        
    differential media  media that contain additives that make it possible to distinguish bacterial colonies based on metabolic activities of the organisms        
    differential staining  staining that uses multiple dyes to differentiate between structures or organisms        
    diffraction  the changing of direction (bending or spreading) that occurs when a light wave interacts with an opening or barrier        
    dikaryotic  having two separate nuclei within one cell        
    dimorphic fungus  a fungus that can take the form of a yeast or a mold, depending on environmental conditions        
    dioecious  refers to sexually reproducing organisms in which individuals have either male or female reproductive organs (not both)        
    diphtheria  serious infection of the larynx, caused by the toxigenic bacterium Corynebacterium diphtheriae        
    diploid  having two copies of each chromosome        
    direct agglutination assay  assay that can be used to detect the agglutination of bacteria by the action of antibodies in patient serum        
    direct antihuman globulin test (DAT)  another name for a direct Coombs’ test        
    direct contact transmission  movement of a pathogen between hosts by physical contact or transfer in droplets at a distance less than one meter        
    direct Coombs’ test  assay that looks for antibodies in vivo against red blood cells caused by various types of infections, drug reactions, and autoimmune disorders        
    direct ELISA  enzyme-linked immunoabsorbent assay in which the antigens are immobilized in the well of a microtiter plate; only a single antibody is used in the test        
    direct fluorescent antibody (DFA) test  FA technique in which the labeled antibody binds to the target antigen        
    direct hemagglutination assay  test that determines the titer of certain bacteria and viruses that causes clumping of red blood cells        
    direct microscopic cell count  counting of cells using a calibrated slide under a light microscope        
    direct repair (light repair or photoreactivation), direct repair  light-dependent mechanism for repairing pyrimidine dimers involving the enzyme photolyase        
    disaccharide  one of two monosaccharides linked together by a glycosidic bond        
    disease  any condition in which the normal structure or function of the body is damaged or impaired        
    disinfectant  antimicrobial chemical applied to a fomite during disinfection that may be toxic to tissues        
    disinfection  protocol that removes potential pathogens from a fomite        
    disk-diffusion method  a technique for measuring of the effectiveness of one or more antimicrobial agents against a known bacterium; involves measuring the zone(s) of inhibition around the chemical agent(s) in a culture of the bacterium        
    dispersion  the separation of light of different frequencies due to different degrees of refraction        
    disulfide bridge  covalent bond between the sulfur atoms of two sulfhydryl side chains        
    DNA gyrase (topoisomerase II)  bacterial topoisomerase that relaxes the supercoiled chromosome to make DNA more accessible for the initiation of replication        
    DNA ligase  enzyme that catalyzes the formation of a covalent phosphodiester linkage between the 3’-OH end of one DNA fragment and the 5’ phosphate end of another DNA fragment        
    DNA packaging  process in which histones or other DNA binding proteins perform various levels of DNA wrapping and attachment to scaffolding proteins to allow the DNA to fit inside a cell        
    DNA polymerase  class of enzymes that adds nucleotides to the free 3’-OH group of a growing DNA chain that are complementary to the template strand        
    DNA primers  short, synthetic, single-stranded DNA fragments of known sequence that bind to specific target sequences within a sample due to complementarity between the target DNA sequence and the primer; commonly used in PCR but may be used in other hybridization techniques        
    DNA probe  a single-stranded DNA fragment that is complementary to part of the gene (DNA or RNA) of interest        
    DNAse  pathogen-produced nuclease that degrades extracellular DNA        
    dosage  amount of medication given during a certain time interval        
    double immunodiffusion  see Ouchterlony assay        
    doubling time  the time it takes for the population to double; also referred to as generation time        
    droplet transmission  direct contact transmission of a pathogen transferred in sneezed or coughed droplets of mucus that land on the new host within a radius of one meter        
    drug resistance  ability of a microbe to persist and grow in the presence of an antimicrobial drug        
    dry-heat sterilization  protocol that involves the direct application of high heat        
    dura mater  tough, outermost membrane that surrounds the brain        
    dynein  motor proteins that interact with microtubules in eukaryotic flagella and cilia        
    dysentery  intestinal inflammation that causes diarrhea with blood and mucus        
    dysuria  urination accompanied by burning, discomfort, or pain        
    E (exit) site  functional site of an intact ribosome that releases dissociated uncharged tRNAs so that they can be recharged with free amino acids        
    East African trypanosomiasis  acute form of African trypanosomiasis caused by Trypanosoma brucei rhodesiense        
    eastern equine encephalitis  serious, but rare, mosquito-borne viral infection of the brain that is found primarily on the Atlantic and Gulf coast states of the United States        
    Ebola virus disease (EVD)  potentially fatal viral hemorrhagic fever found primarily in western Africa and transmitted through contact with body fluids        
    eclipse phase  period after viral infection during which the infective virus is not detected, either intracellularly or extracellularly, and biosynthesis is occurring        
    ectoplasm  outer, more gelatinous layer of cytoplasm under a protist cell membrane        
    edema  swelling due to accumulation of fluid and protein in tissue as a result of increased permeability of capillary walls during an inflammatory response; chronic edema can also result from blockage of lymphatic vessels, as in the case of elephantiasis        
    effector cells  activated cells of cellular immunity that are involved in the immediate immune response, primarily to defend the body against pathogens        
    electron carrier  cellular molecule that accepts high-energy electrons from reduced molecules like foods and later serves as an electron donor in subsequent redox reactions        
    electron microscope  a type of microscope that uses short-wavelength electron beams rather than light to increase magnification and resolution        
    electron transport system (ETS)  series of membrane-associated protein complexes and associated mobile accessory electron carriers important in the generation of the proton motive force required for ATP production by chemiosmosis; the last component involved in the cellular respiration of glucose        
    electroporation  a genetic engineering technique in which cells are exposed to a short electric pulse, inducing them to take up DNA molecules from their environment        
    elementary bodies  metabolically and reproductively inactive, endospore-like form of intracellular bacteria that spreads infection outside of cells        
    elongation in DNA replication  stage of DNA replication during which DNA polymerase adds nucleotides, complementary to the parental strand, to the 3’ end of a growing DNA strand        
    elongation in transcription  stage of transcription during which RNA polymerase extends the RNA molecule by adding RNA nucleotides, complementary to the template DNA strand        
    elongation of translation  stage of translation during which amino acids are added one by one to the C-terminus of the growing polypeptide        
    Embden-Meyerhof-Parnas (EMP) pathway  type of glycolysis found in animals and the most common in microbes        
    emerging infectious disease  a disease that is new to the human population or has increased in prevalence over the previous 20 years        
    enantiomers  stereoisomers that are mirror images of each other and nonsuperimposable        
    encephalitis  inflammation of the tissues of the brain        
    encystment  the process of forming a cyst        
    endemic disease  an illness that is constantly present (often at low levels) in a population        
    endergonic reaction, endergonic reactions  chemical reaction that requires energy beyond activation energy to occur        
    endocarditis  inflammation of the endocardium, especially the heart valves        
    endocrine function  refers to a cytokine signal released from a cell and carried by the bloodstream to a distant recipient cell        
    endocytosis  the uptake of molecules through plasma membrane invagination and vacuole/vesicle formation        
    endomembrane system  a series of organelles (endoplasmic reticulum, Golgi apparatuses, lysosomes, and transport vesicles) arranged as membranous tubules, sacs, and disks that synthesize many cell components        
    endoplasm  inner, more fluid layer of cytoplasm under a protist cell membrane (inside of the ectoplasm)        
    endoplasmic reticulum  part of the endomembrane system that is an interconnected array of tubules and flattened sacs with a single lipid bilayer that may be either rough or smooth; important in synthesizing proteins and lipids        
    endospore  a cellular structure formed by some bacteria in response to adverse conditions; preserves DNA of the cell in a dormant state until conditions are favorable again        
    endospore staining  a differential staining technique that uses two stains to make bacterial endospores appear distinct from the rest of the cell        
    endosymbiotic theory  the theory that mitochondria and chloroplasts arose as a result of prokaryotic cells establishing a symbiotic relationship within a eukaryotic host        
    endothelia  layer of epithelial cells lining blood vessels, lymphatics, the blood-brain barrier, and some other tissues        
    endotoxin  lipid A component of lipopolysaccharides in the outer membrane of gram-negative bacteria        
    enriched media  media that contain additional essential nutrients to support growth        
    enrichment culture  media providing growth conditions that favor the expansion of an organism present in low numbers        
    enteric  bacteria of the family Enterobacteriaceae, which live in the human intestinal tract        
    enteritis  inflammation of the lining of the intestine        
    enterobiasis  intestinal infection caused by the pinworm Enterobius vermicularis        
    enterohemorrhagic E. coli (EHEC)  E. coli bacteria that cause severe gastrointestinal illness with potential serious complications such as hemolytic uremic syndrome        
    enteroinvasive E. coli (EIEC)  E. coli bacteria that cause relatively mild gastrointestinal illness        
    enteropathogenic E. coli (EPEC)  E. coli bacteria that cause serious gastrointestinal illness        
    enterotoxigenic E. coli (ETEC)  E. coli bacteria that cause a relatively mild illness commonly called traveler’s diarrhea        
    enterotoxin  toxin that affects the intestines        
    Entner-Doudoroff (ED) pathway  alternative glycolytic pathway used by some bacteria        
    enveloped virus  a virus formed with a nucleic-acid packed capsid surrounded by a lipid layer        
    enzyme, enzymes  catalyst for biochemical reactions inside cells        
    enzyme immunoassay (EIA)  type of assay wherein an enzyme is coupled to an antibody; addition of a chromogenic substrate for the antibody allows quantification or identification of the antigen bound by the antibody        
    enzyme-linked immunosorbent assay (ELISA)  specialized form of EIA in which either the primary antibody or the antigen is first attached to a solid surface such as the well of a microtiter plate        
    eosinophils  leukocytes with granules containing histamine and major basic protein; facilitate allergic responses and protection against parasitic protozoa and helminths        
    epidemic disease  an illness with a higher-than-expected incidence in a given period within a given population        
    epidemic typhus  severe and sometimes fatal infection caused by Rickettsia prowazekii and transmitted by body lice        
    epidemiology  the study of where and when infectious diseases occur in a population and how they are transmitted and maintained in nature        
    epidermis  the outermost layer of human skin        
    epididymis  coiled tube that collects sperm from the testes and passes it on to the vas deferens        
    epididymitis  inflammation of the epididymis caused by a bacterial infection        
    epigenetic regulation  chemical modification of DNA or associated histones to influence transcription        
    epiglottis  flap of cartilage that covers the larynx during swallowing; diverts food to the esophagus and prevents it from entering the respiratory tract        
    epiglottitis  inflammation of the epiglottis        
    epiphyte  a plant that grows on another plant        
    epitope  smaller exposed region on an antigen that is recognized by B-cell and T-cell receptors and antibodies        
    Epsilonproteobacteria  class of Proteobacteria that are microaerophilic        
    equivalence zone  region where the antibody–antigen ratio produces the greatest amount of precipitin in a precipitin reaction        
    erysipelas  a skin infection, typically caused by Streptococcus pyogenes, that presents as a red, large, intensely inflamed patch of skin involving the dermis, usually with clear borders, typically on the legs or face        
    erythema nodosum  a condition that causes inflammation in the subcutaneous fat cells of the hypodermis resulting in red nodules        
    erythema  redness at the site of inflammation, usually due to dilation of blood vessels in the area to help bring in white blood cells        
    erythrocyte  red blood cell        
    erythrogenic toxin  exotoxin produced by some strains of Streptococcus pyogenes; activity of the toxin can produce the characteristic rash of scarlet fever        
    erythromycin  protein synthesis inhibitor of the macrolide class that is often used as an alternative to penicillin        
    eschar  a localized mass of dead skin tissue        
    Etest  simple, rapid method for determining MIC, involving commercially available plastic strips that contain a gradient of an antimicrobial and are placed on an agar plate inoculated with a bacterial lawn        
    etiologic agent  the pathogen or substance responsible for causing a particular disease; causative agent        
    etiology  the science of the causes of disease        
    Eukarya  the domain of life that includes all unicellular and multicellular organisms with cells that contain membrane-bound nuclei and organelles        
    eukaryote  an organism made up of one or more cells that contain a membrane-bound nucleus and organelles        
    eukaryotic cell  has a nucleus surrounded by a complex nuclear membrane that contains multiple, rod-shaped chromosomes        
    eustachian tube  small passage between the nasopharynx and the middle ear that allows pressure to equalize across the tympanic membrane        
    excystment  the process of emerging from a cyst        
    exergonic reaction, exergonic reactions  chemical reaction that does not require energy beyond activation energy to proceed; releases energy when the reaction occurs        
    exocytosis  the release of the contents of transport vesicles to the cell’s exterior by fusion of the transport vesicle’s membrane with the plasma membrane        
    exoenzyme  secreted enzyme that enhances the ability of microorganisms to invade host cells        
    exon  protein-coding sequence of a eukaryotic gene that is transcribed into RNA and spliced together to code for a polypeptide        
    exonuclease  enzymatic activity that removes RNA primers in DNA introduced by primase        
    exotoxin  biologically active product that causes adverse changes in the host cells        
    experimental epidemiology  the use of laboratory and clinical studies to directly study disease in a population        
    experimental study  a type of scientific study that involves manipulation of the study subjects by the researcher through application of specific treatments hypothesized to affect the outcome while maintaining rigorously controlled conditions        
    exposure  contact between potential pathogen and host; also called contamination or contact        
    extended-spectrum β-lactamases (ESBLs)  β-lactamases carried by some gram-negative bacteria that provide resistance to all penicillins, cephalosporins, monobactams, and β-lactamase-inhibitor combinations, but not carbapenems        
    extensively drug resistant Mycobacterium tuberculosis (XDR-TB)  strains of M. tuberculosis that are resistant to rifampin and isoniazid, and also are resistant to any fluoroquinolone and at least one of three other drugs (amikacin, kanamycin, or capreomycin)        
    extracellular matrix  material composed of proteoglycans and fibrous proteins secreted by some eukaryotic cells that lack cell walls; helps multicellular structures withstand physical stresses and coordinates signaling from the external surface of the cell to the interior of the cell        
    extracellular polymeric substances (EPS)  hydrated gel secreted by bacteria in a biofilm containing polysaccharides, proteins, nucleic acids, and some lipids        
    extrachromosomal DNA  additional molecules of DNA distinct from the chromosomes that are also part of the cell’s genome        
    extravasation  process by which leukocytes pass through capillary walls to reach infected tissue; also called diapedesis        
    F (recipient) cell  E. coli cell lacking the F plasmid and thus incapable of forming a conjugation pilus but capable of receiving the F plasmid during conjugation        
    F pilus (F pili)  specialized type of pilus that aids in DNA transfer between cells; conjugation pilus of E. coli        
    F plasmid (fertility factor)  bacterial plasmid in E. coli containing genes encoding the ability to conjugate, including genes encoding the formation of the conjugation pilus        
    F’ plasmid  integrated F plasmid imprecisely excised from the chromosome; carries with it some chromosomal DNA adjacent to the integration site        
    F+ (donor) cell  E. coli cell containing the F plasmid, capable of forming a conjugation pilus        
    Fab region  arm of an antibody molecule that includes an antigen-binding site        
    facultative anaerobe  organism that grows better in the presence of oxygen but can proliferate in its absence        
    false negative  negative result to a test for an infection or condition (e.g., presence of antigen, antibody, or nucleic acid) when the infection or condition is actually present        
    false positive  positive result to a test for an infection or condition (e.g., presence of antigen, antibody, or nucleic acid) when the infection or condition is actually absent        
    fastidious organism  organism that has extensive growth requirements        
    fatty acid  lipid that contains long-chain hydrocarbons terminated with a carboxylic acid functional group        
    fatty acid methyl ester (FAME) analysis  technique in which the microbe’s fatty acids are extracted, converted to volatile methyl esters, and analyzed by gas chromatography, yielding chromatograms that may be compared to reference data for identification purposes        
    Fc region  region on the trunk of an antibody molecule involved in complement activation and opsonization        
    feedback inhibition  mechanism of regulating metabolic pathway whereby the product of a metabolic pathway noncompetitively binds to an enzyme early on in the pathway, temporarily preventing the synthesis of the product        
    fermentation  process that uses an organic molecule as a final electron acceptor to regenerate NAD+ from NADH such that glycolysis can continue        
    fever  system-wide sign of inflammation that raises the body temperature and stimulates the immune response        
    fifth disease  a highly contagious illness, more commonly affecting children, marked by a distinctive “slapped-cheek” rash and caused by parvovirus B19        
    fimbriae  filamentous appendages found by the hundreds on some bacterial cells; they aid adherence to host cells        
    fine focusing knob  a knob on a microscope that produces relatively small movements to adjust focus        
    fixation  the process by which cells are killed and attached to a slide        
    flagella  long, rigid, spiral structures used by prokaryotic cells for motility in aqueous environments; composed of a filament made of flagellin, a hook, and motor (basal body) that are attached to the cell envelope        
    flagella staining  a staining protocol that uses a mordant to coat the flagella with stain until they are thick enough to be seen        
    flagellum (eukaryotic) (plural: flagella)  long, whip-like, filamentous external structure found on some eukaryotic cells; composed of microtubules in a 9+2 arrangement; used for locomotion        
    flavin adenine dinucleotide (FAD/FADH2)  oxidized/reduced forms of an electron carrier in cells        
    flocculant  visible aggregation that forms between a substance in suspension (e.g., lipid in water) and antibodies against the substance        
    flow cytometry  technique analyzing cells for fluorescence intensity; specific subsets of cells are usually labeled in some way prior to the analysis        
    fluconazole  antifungal drug of the imidazole class that is administered orally or intravenously for the treatment of several types of systemic yeast infections        
    fluid mosaic model  refers to the ability of membrane components to move fluidly within the plane of the membrane, as well as the mosaic-like composition of the components        
    flukes  any of the parasitic nonsegmented flatworms (trematodes) that have an oral sucker and sometimes a second ventral sucker; they attach to the inner walls of intestines, lungs, large blood vessels, or the liver in human hosts        
    fluorescence microscope  a microscope that uses natural fluorochromes or fluorescent stains to increase contrast        
    fluorescence-activated cell sorter (FACS)  technique for using a flow cytometer to physically separate cells into two populations based on fluorescence intensity        
    fluorescent antibody (FA) techniques  suite of assays that use a fluorescently labeled antibody to bind to and so make an antigen easy to visualize        
    fluorescent enzyme immunoassay (FEIA)  EIA in which the substrate is a fluorogen that becomes fluorescent following reaction with the enzyme        
    fluorescent  the ability of certain materials to absorb energy and then immediately release that energy in the form of light        
    fluorochromes  chromophores that fluoresce (absorb and then emit light)        
    fluorogen  nonfluorescent molecule that becomes fluorescent on enzyme or laser activation        
    fluorophore  molecule that fluoresces when excited by light        
    fluoroquinolones  class of synthetic antimicrobials that inhibit the activity of DNA gyrase, preventing DNA replication        
    focal infection  infection in which the pathogen causes infection in one location that then spreads to a secondary location        
    focal length  the distance from the lens to the image point when the object is at a definite distance from the lens (this is also the distance to the focal point)        
    focal point  a property of the lens; the image point when light entering the lens is parallel (i.e., the object is an infinite distance from the lens)        
    foliose lichens  lichens that have lobes that may appear to resemble leaves        
    folliculitis  a skin infection characterized by localized inflammation of hair follicles, typically producing an itchy red rash        
    fomite  inanimate item that may harbor microbes and aid in disease transmission        
    foodborne disease  disease that is transmitted through contaminated food        
    fragmentation  newly formed cells split away from the parent filament in actinomycetes and cyanobacteria        
    frameshift mutation  mutation resulting from either an insertion or a deletion in a number of nucleotides that, if not a multiple of three, changes every amino acid after the mutation        
    free ribosome  eukaryotic 80S ribosome found in the cytoplasm; synthesizes water-soluble proteins        
    frequency  the rate of vibration for a light wave or other electromagnetic wave        
    fruticose lichens  lichens that are generally branched with a rounded appearance        
    functional groups  specific groups of atoms that may occur within a molecule, conferring specific chemical properties        
    fungi  (singular: fungus) any of various unicellular or multicellular eukaryotic organisms, typically having cell walls made out of chitin and lacking photosynthetic pigments, vascular tissues, and organs        
    fungicide  chemical or physical treatment that kills fungi        
    fungistatic  having the ability to inhibit fungal growth, generally by means of chemical or physical treatment        
    furuncle  a small, purulent skin lesion; sometimes called a boil        
    fusion inhibitor  antiviral drug that blocks the fusion of HIV receptors to the coreceptors required for virus entry into the cell, specifically, chemokine receptor type 5        
    Gammaproteobacteria  class of Proteobacteria that is very diverse and includes a number of human pathogens        
    gas gangrene  rapidly spreading infection of necrotic tissues caused by the gram-positive anaerobe Clostridium perfringens and other Clostridium spp.        
    gastritis  inflammation of the lining of the stomach        
    gastroenteritis  inflammation of the lining of the stomach and intestine        
    gene expression  production of proteins from the information contained in DNA through the processes of transcription and translation        
    gene gun  an apparatus that shoots gold or tungsten particles coated with recombinant DNA molecules at high speeds into plant protoplasts        
    gene silencing  a genetic engineering technique in which researchers prevent the expression of a particular gene by using small interfering RNAs (siRNAs) or microRNAs (miRNAs) to interfere with translation        
    gene therapy  a form of treatment for diseases that result from genetic mutations; involves the introduction of nonmutated, functional genes into the genome of the patient, often by way of a viral vector        
    generalized transduction  transfer of a random piece of bacterial chromosome DNA by the phage        
    generation time  see doubling time        
    genes  segments of DNA molecules that code for proteins or stable RNA molecules        
    genetic code  correspondence between mRNA nucleotide codons and the translated amino acids        
    genetic engineering  the direct alteration of an organism’s genetics to achieve desirable traits        
    genital herpes  an STI caused by the herpes simplex virus        
    genital warts  soft, pink, irregular growths that develop in the external genitalia or anus as a result of human papillomavirus infection        
    genome  entire genetic content of a cell        
    genomic library  a repository of an organism’s entire genome maintained as cloned fragments in the genomes of strains of a host organism        
    genomics  the study and comparison of entire genomes, including the complete set of genes, their nucleotide sequence and organization, and their interactions within a species and with other species        
    genotype  full collection of genes that a cell contains within its genome        
    germ theory of disease  the theory that many diseases are the result of microbial infection        
    germination  process of an endospore returning to the vegetative state        
    Ghon complex  calcified lesion containing Mycobacterium tuberculosis; forms in the lungs of patients with tuberculosis        
    giardiasis  intestinal infection caused by Giardia lamblia        
    gingivitis  inflammation of the gums that can cause bleeding        
    glial cell  assists in the organization of neurons, provides a scaffold for some aspects of neuron function, and aids in recovery from neural injury        
    glomerulonephritis  a type of kidney infection involving the glomeruli of the nephrons        
    glomerulus  capillary bed in the nephron of the kidney that filters blood to form urine        
    glycocalyx  cell envelope structure (either capsules or slime layer) outside the cell wall in some bacteria; allows bacteria to adhere to surfaces, aids in biofilm formation, and provides protection from predation        
    glycogen  highly branched storage polysaccharide in animal cells and bacteria        
    glycolipid  complex lipid that contains a carbohydrate moiety        
    glycolysis  first step in the breakdown of glucose, the most common example of which is the Embden-Meyerhoff-Parnas pathway, producing two pyruvates, two NADH molecules, and two (net yield) ATP per starting glucose molecule        
    glycopeptides  class of antibacterials that inhibit cell wall synthesis by binding to peptidoglycan subunits and blocking their insertion into the cell wall backbone, as well as blocking transpeptidation        
    glycoprotein  conjugated protein with a carbohydrate attached        
    glycosidic bond  forms between the hydroxyl groups of two sugar molecules        
    Golgi apparatus  an organelle of the endomembrane system that is composed of a series of flattened membranous disks, called dictyosomes, each having a single lipid bilayer, that are stacked together; important in the processing of lipids and proteins        
    gonorrhea  a common STI of the reproductive system caused by Neisseria gonorrhoeae        
    graft-versus-host disease  specific type of transplantation reaction in which a transplanted immune system (e.g., a bone marrow transplant) contains APCs and T cells that are activated and attack the recipient’s tissue        
    Gram stain procedure  a differential staining technique that distinguishes bacteria based upon their cell wall structure        
    granulocytes  leukocytes found in the peripheral blood that are characterized by numerous granules in the cytoplasm; granulocytes include neutrophils, eosinophils, and basophils        
    granuloma  walled-off area of chronically inflamed tissue containing microbial pathogens, macrophages, and cellular materials unable to be eliminated        
    granulomatous amoebic encephalitis (GAE)  serious brain infection of immunocompromised individuals caused by Acanthamoeba or Balamuthia mandrillaris        
    granzymes  proteases released from a natural killer cell that enter the cytoplasm of a target cell, inducing apoptosis        
    Graves disease  hyperthyroidism caused by an autoimmune disease affecting thyroid function        
    green nonsulfur bacteria  similar to green sulfur bacteria but use substrates other than sulfides for oxidation        
    green sulfur bacteria  phototrophic, anaerobic bacteria that use sulfide for oxidation and produce large amounts of green bacteriochlorophyll        
    growth curve  a graph modeling the number of cells in a culture over time        
    guanine  purine nitrogenous base found in nucleotides        
    Guillain-Barré syndrome  an autoimmune disease, often triggered by bacterial and viral infections, characterized by the destruction of myelin sheaths around neurons, resulting in flaccid paralysis        
    gummas  granulomatous lesions that develop in tertiary syphilis        
    hair follicle  a structure embedded in the dermis from which hair grows        
    halophile  organism that depends on high concentrations of salt in the environment to grow        
    halotolerant  organism that grows in the presence of high salt concentration but does not require it        
    Hansen’s Disease  chronic bacterial infection of peripheral nervous tissues caused by the acid-fast bacterium, Mycobacterium leprae; also known as leprosy        
    hantavirus pulmonary syndrome  acute lung infection by a hantavirus following inhalation of aerosols from the urine or feces of infected rodents        
    haploid  having one copy of each chromosome        
    hapten  a molecule that is too small to be antigenic alone but becomes antigenic when conjugated to a larger protein molecule        
    hard chancre  a generally painless ulcer that develops at the site of infection in primary syphilis        
    Hashimoto thyroiditis  hypothyroidism caused by an autoimmune disease affecting thyroid function        
    healthcare-associated infection (HAI)  an infection acquired in a hospital or other health-care facility unrelated to the reason for which the patient was initially admitted; nosocomial infection        
    heavy chains  longest identical peptide chains in antibody molecules (two per antibody monomer), composed of variable and constant region segments        
    helical virus  cylindrical or rod shaped        
    helicase  enzyme that unwinds DNA by breaking the hydrogen bonds between the nitrogenous base pairs, using ATP        
    helminth  a multicellular parasitic worm        
    helper T cells  class of T cells that is the central orchestrator of the cellular and humoral defenses of adaptive immunity and the cellular defenses of innate immunity        
    hemagglutination  visible clumping of red blood cells that can be caused by some viruses, bacteria, and certain diseases in which antibodies are produced that bind to self-red blood cells        
    hematopoiesis  formation, development, and differentiation of blood cells from pluripotent hematopoietic stem cells        
    hematuria  condition in which there is blood in the urine        
    hemolysin  class of exotoxin that targets and lyses red blood cells, as well as other cells        
    hemolytic disease of the newborn (HDN)  type II hypersensitivity reaction that occurs when maternal anti-Rh antibodies cross the placenta and target fetal Rh+ red blood cells for lysis        
    hemolytic transfusion reaction (HTR)  condition resulting after an incompatible blood transfusion; caused by type II hypersensitivity reaction and destruction of red blood cells        
    hemorrhagic fever with renal syndrome  serious hemorrhagic fever caused by hantavirus infection        
    HEPA filter  high-efficiency particulate air filter with an effective pore size that captures bacterial cells, endospores, and viruses as air passes through, removing them from the air        
    hepatitis  inflammation of the liver        
    herd immunity  a reduction in disease prevalence brought about when few individuals in a population are susceptible to an infectious agent        
    herpes keratitis  eye infection caused by herpes simplex virus        
    herpes simplex virus type 2 (HSV-2)  the type of herpesvirus most commonly associated with genital herpes        
    herpetic gingivostomatitis  inflammation of the mouth and gums often caused by the HSV-1 virus        
    heterolactic fermentation  process producing a mixture of lactic acid, ethanol and/or acetic acid, and CO2 as fermentation products; the microbes that do this use pentose phosphate pathway glycolysis, which is why they generate multiple fermentation products        
    heterotroph, heterotrophs  organism that uses fixed organic carbon compounds as its carbon source        
    hexose monophosphate shunt  see pentose phosphate pathway        
    Hfr cell  E. coli cell in which an F plasmid has integrated into the host cell’s chromosome        
    high G+C gram-positive bacteria  bacteria that have more than 50% guanine and cytosine nucleotides in their DNA        
    high-energy phosphate bond  bond between the negatively charged phosphate groups that holds a lot of potential energy        
    histamine  proinflammatory molecule released by basophils and mast cells in response to stimulation by other cytokines and chemical mediators        
    histones  DNA-binding proteins found in eukaryotes and archaea that aid in orderly packaging of chromosomal DNA        
    histoplasmosis  fungal disease caused by the dimorphic fungus Histoplasma capsulatum        
    holoenzyme  enzyme with a bound cofactor or coenzyme        
    holozoic  refers to protozoans that consume food particles through phagoctytosis        
    homolactic fermentation  process producing only lactic acid as a fermentation product; the microbes that do this use Embden-Meyerhof-Parnas glycolysis        
    hookworm infection  soil-transmitted intestinal infection caused by the nematodes Necator americanus and Ancylostoma doudenale        
    horizontal direct transmission  movement of a pathogen from one host to another (excluding mother to embryo, fetus, or infant) in a population through physical contact or through droplet transmission        
    horizontal gene transfer  introduction of genetic material from one organism to another organism within the same generation        
    host range  the types of host cells that a particular virus is able to infect        
    HTST  high-temperature short-time pasteurization is a method of pasteurization commonly used for milk in which the milk is exposed to a temperature of 72 °C for 15 seconds        
    human African trypanosomiasis  serious infection caused by Trypanosoma brucei and spread by the bite of the tsetse fly        
    human granulocytic anaplasmosis  zoonotic tickborne disease caused by the obligate intracellular pathogen Anaplasma phagocytophilum        
    human immunodeficiency virus (HIV)  retrovirus responsible for acquired immune deficiency syndrome (AIDS) in humans        
    human papillomavirus (HPV)  a group of common sexually transmitted viruses that may be associated with genital warts or with cervical cancer        
    humanized monoclonal antibodies  chimeric antibodies with mouse variable regions and human constant regions        
    humoral immunity  adaptive immunity mediated by antibodies produced by B cells        
    hyaluronidase  enzyme produced by pathogens that degrades hyaluronic acid between adjacent cells in connective tissue        
    hybridization  the joining of two complementary single-stranded DNA molecules        
    hybridoma  clones of cell produced by fusing a normal B cell with a myeloma cell that is capable of producing monoclonal antibodies indefinitely        
    hydatid disease  cystic echinococcosis, an infection caused by the tapeworm Echinococcus granulosus        
    hydrophilic  “water loving”; refers to a polar molecule or portion of a molecule capable of strong attraction to water molecules        
    hydrophobic  “water fearing”; refers to a nonpolar molecule or portion of a molecule not capable of strong attraction to water molecules        
    hypersensitivity pneumonitis (HP)  type III and IV hypersensitivities in the lungs that are caused by environmental or occupational exposure to allergens such as mold and dust        
    hypersensitivity  potentially damaging immune response against an antigen        
    hyperthermophile  a microorganism that has an optimum growth temperature close to the temperature of boiling water        
    hypertonic medium  an environment in which the solute concentration outside a cell exceeds that inside the cell, causing water molecules to move out of the cell, resulting in crenation (shriveling) or plasmolysis.        
    hyphae  tubular, filamentous structures that makes up most fungi        
    hypodermis  the layer of tissue under the dermis, consisting primarily of fibrous and adipose connective tissue        
    hypotonic medium  an environment in which the solute concentration inside a cell exceeds that outside the cell, causing water molecules to move into the cell, possibly leading to swelling and possibly lysis        
    iatrogenic disease  disease caused by or acquired during a medical procedure        
    icosahedral  three-dimensional, 20-sided structure with 12 vertices        
    IgA  antibody dimer primarily found in breast milk, mucus, saliva, and tears        
    IgD  membrane-body antibody monomer functioning as receptor on the surface of B cells        
    IgE  antibody monomer involved in defense against parasites and allergic reactions        
    IgG  antibody monomer most abundant in serum; able to cross placenta; most versatile class of antibody in terms of function        
    IgM  antibody that is a monomer when functioning as a receptor on surface of B cells but a pentamer when secreted in response to specific pathogens; first antibody to respond during primary and secondary responses        
    illuminator  the light source on a microscope        
    image point (focus)  a property of the lens and the distance of the object to the lens; the point at which an image is in focus (the image point is often called the focus)        
    imidazoles  class of antifungal drugs that inhibit ergosterol biosynthesis        
    immune complex  large group of antigens bound by antibodies; large enough to settle out of fluid suspension        
    immunochromatographic assay  assay in which fluids are pulled through test strips by capillary action and antigen captured by mobile antibody-colored bead conjugates; a second, fixed antibody localizes the colored bead, allowing visualization        
    immunocytochemistry (ICC)  staining technique in which cells are fixed and holes dissolved in the membrane to allow passage of labeled antibodies to bind specific intracellular targets        
    immunoelectrophoresis (IEP)  assay following protein electrophoresis (PAGE) of serum, in which antisera against specific serum proteins are added to troughs cut parallel to the electrophoresis track, causing the formation of precipitin arcs        
    immunofiltration  technique in which antibody or antigen can be concentrated by passing fluids through porous membranes, and target molecules are captured as they pass        
    immunofluorescence  a technique that uses a fluorescence microscope and antibody-specific fluorochromes to determine the presence of specific pathogens in a specimen        
    immunoglobulin  antibody        
    immunohistochemistry (IHC)  staining technique in which labeled antibodies are bound to specific cells in a tissue section        
    immunology  the study of the immune system        
    immunostain  use of EIA technology to deliver stain to particular cells in a tissue (immunohistochemistry) or specific targets within a cell (immunocytochemistry)        
    impetigo  a skin infection that may result in vesicles, blisters, or bullae especially around the mouth, commonly caused by Staphylococcus aureusS. pyogenes, or a combination of both S. aureus and S. pyogenes        
    in vitro  outside the organism in a test tube or artificial environment        
    in vivo  inside the organism        
    inactivated vaccine  vaccine composed of whole pathogen cells or viruses that have been killed or inactivated through treatment with heat, radiation, or chemicals        
    incidence  the number of individuals with new infections of a particular disease in a given period of time        
    inclusion conjunctivitis  inflammation of the conjunctiva in newborns caused by Chlamydia trachomatis transmitted during childbirth        
    inclusions  prokaryotic cell cytoplasmic structures for storing specific nutrients and other resources needed by cells        
    incubation period  the first stage of acute disease, during which the pathogen begins multiplying in the host and signs and symptoms are not observable        
    indirect agglutination assay  assay that can be used to detect the agglutination of small latex beads; beads may be coated with antigen when looking for the presence of specific antibodies, or with antibody when looking for the presence of antigen        
    indirect antiglobulin test (IAT)  see indirect Coombs’ test        
    indirect contact transmission  transfer of an infectious agent between hosts through contact with a fomite        
    indirect Coombs’ test  assay, performed in vitro prior to blood transfusions, that looks for antibodies against red blood cell antigens (other than the A and B antigens) that are unbound in a patient’s serum        
    indirect ELISA  EIA in which an antigen from a pathogen is first attached to the wells of a microtiter plate; the antigen then captures antibodies from patient serum to determine whether the patient currently has or previosly had the disease        
    indirect fluorescent antibody test  assay for antigen-specific antibodies wherein the antigen captures the antibody, which is subsequently detected using a labeled anti-immunoglobulin mAb        
    induced mutation  mutation caused by a mutagen        
    inducer  small molecule that either activates or represses transcription        
    inducible operon  bacterial operon, typically containing genes encoding enzymes in a degradative pathway, whose expression is induced by the substrate to be degraded when the substrate is available for the cell to use, but that is otherwise repressed in the absence of the substrate        
    induction  prophage DNA is excised from the bacterial genome        
    infection  the successful colonization of a microorganism within a host        
    infectious arthritis (septic arthritis)  inflammation of joint tissues in response to a microbial infection        
    infectious disease  disease caused by a pathogen        
    infectious mononucleosis  common and mild infection caused by Epstein-Barr virus (HHV-4) or cytomegalovirus (HHV-5); transmitted by direct contact with body fluids such as saliva        
    inflammation  innate nonspecific immune response characterized by erythema, edema, heat, pain, and altered function, typically at the site of injury or infection but sometimes becoming systemic.        
    influenza  highly contagious and acute viral disease of the respiratory tract caused by the influenza virus        
    initiation factors  proteins that participate in ribosome assembly during initiation        
    initiation of DNA replication  stage of replication during which various proteins bind to the origin of replication to begin the replication process        
    initiation of transcription  stage of transcription during which RNA polymerase binds to a promoter and transcription begins        
    initiation of translation  stage of translation during which an initiation complex composed of the small ribosomal subunit, the mRNA template, initiation factors, GTP, and a special initiator tRNA forms, and the large ribosomal subunit then binds to the initiation complex        
    inoculum  small number of cells added to medium to start a culture        
    inorganic phosphate (Pi)  single phosphate group in solution        
    insertion  type of mutation involving the addition of one or more bases into a DNA sequence        
    integrase inhibitors  antiviral drugs that block the activity of the HIV integrase responsible for recombination of a DNA copy of the viral genome into the host cell chromosome        
    intercalating agent, intercalating agents  molecule that slides between the stacked nitrogenous bases of the DNA double helix, potentially resulting in a frameshift mutation        
    interference  distortion of a light wave due to interaction with another wave        
    interferons  cytokines released by cells that have been infected with a virus; stimulate antiviral responses in nearby cells as well as the cells secreting the interferons        
    interleukins  cytokines largely produced by immune system cells that help coordinate efforts against invading pathogens        
    intermediate filament  one of a diverse group of cytoskeletal fibers that act as cables within the cell and anchor the nucleus, comprise the nuclear lamina, or contribute to the formation of desmosomes        
    intermediate host  a host in which a parasite goes through some stages of its life cycle before migrating to the definitive host        
    intermittent common source spread  a mode of disease transmission in which every infection originates from the same source and that source produces infections for a period before stopping and then starting again        
    interphase period of the cell cycle leading up to mitosis; includes G1, S, and G2 phases (the interim period between two consecutive cell divisions        
    intertrigo  a rash that occurs in a skin fold        
    intestinal fluke  a trematode worm that infects the intestine, often caused by Fasciolopsis buski        
    intracellular targeting toxin  see A-B exotoxin        
    intrinsic growth rate  genetically determined generation time under specific conditions for a bacterial strain        
    intron  intervening sequence of a eukaryotic gene that does not code for protein and whose corresponding RNA sequences are removed from the primary transcript during splicing        
    intubation  placement of a tube into the trachea, generally to open the airway or to administer drugs or oxygen        
    in-use test  a technique for monitoring the correct use of disinfectants in a clinical setting; involves placing used, diluted disinfectant onto an agar plate to see if microbial colonies will grow        
    invasion  dissemination of a pathogen through local tissues or throughout the body        
    iodophor  compound in which iodine is complexed to an organic molecule, increasing the stability and efficacy of iodine as a disinfectant        
    ionizing radiation  high-energy form of radiation that is able to penetrate surfaces and sterilize materials by damaging microbial cell components and DNA        
    ischemia  condition marked by the inadequate flow of blood to the tissues        
    isograft  tissue grafted from one monozygotic twin to another        
    isohemagglutinins  IgM class antibodies produced against A or B red blood cell antigens        
    isomers  molecules that have the same atomic makeup but differ in the structural arrangement of the atoms        
    isoniazid  antimetabolite that inhibits biosynthesis of mycolic acid; used for the treatment of mycobacterial infections        
    isoprenoid  branched lipid derived from five-carbon isoprene molecules        
    isotonic medium  a solution in which the solute concentrations inside and outside the cell are approximately equal, thereby creating no net movement of water molecules across the cell membrane        
    ivermectin  antihelminthic drug of the avermectin class that binds to invertebrate glutamate-gated chloride channels to block neuronal transmission in helminths        
    Japanese encephalitis  arboviral disease caused by the Japanese encephalitis virus (JEV) and endemic to Asia        
    jaundice  yellowish color of the skin and mucous membranes caused by excessive bilirubin caused by a failure of the liver to effectively process the breakdown of hemoglobin        
    karyokinesis mitotic nuclear division        
    keratin  a fibrous protein found in hair, nails, and skin        
    keratitis  inflammation of the cornea        
    keratoconjunctivitis  inflammation of both the cornea and the conjunctiva        
    kidney  organ that filters the blood, producing urine        
    Kinyoun technique  a method of acid-fast staining that does not use heat to infuse the primary stain, carbolfuchsin, into acid-fast cells        
    Kirby-Bauer disk diffusion test  simple, rapid method for determining susceptibility and resistance of a bacterial pathogen to antibacterial drugs. The test involves drug-impregnated disks placed on an agar plate inoculated with a bacterial lawn.        
    Koplik’s spots  white spots that form on the inner lining of the cheek of patients with measles        
    Krebs cycle  cyclic pathway during which each two-carbon unit entering the cycle is further oxidized, producing three NADH, one FADH2, and one ATP by substrate-level phosphorylation, releasing two CO2 molecules and regenerating the molecule used in the first step; also called the citric acid cycle or the tricarboxylic acid cycle        
    kuru  rare form of transmissible spongiform encephalopathy endemic to Papua New Guinea        
    lacrimal duct  connects the lacrimal gland to the lacrimal sac        
    lacrimal gland  a gland situated above the eye that secretes tears        
    lacrimal punctum  opening in each upper and lower eyelid        
    lacrimal sac  a to a reservoir for tears; also known as the dacrocyst or tear sac        
    lag period  the time between antigen exposure and production of antibodies        
    lag phase  interval before exponential growth of a microbial population during which cells adjust to a new environment        
    lagging strand  strand of DNA made discontinuously by DNA polymerase        
    laryngitis  inflammation of the larynx        
    laryngopharynx  lower portion of the pharynx that connects to the larynx        
    larynx  region of the respiratory tract containing the vocal cords; also referred to as the voice box        
    latent disease  disease that goes into a dormant nonreplicative state after the acute disease and can persist in this state for years, with the risk of reactivation back into acute disease        
    latent virus  virus that remains dormant in the host genome        
    lateral flow test  see immunochromatographic assays        
    leading strand  strand of DNA made continuously in the 5’ to 3’ direction by DNA polymerase        
    Legionnaires disease  atypical pneumonia occurring in older individuals; caused by the inhalation of Legionella pneumophila aerosolized in water        
    leishmaniasis  protozoan infection caused by Leishmania spp. and transmitted by sand flies        
    leprosy  see Hansen’s disease        
    leptospirosis  bacterial infection of the kidney caused by Leptospira spp.; may spread to the liver, lungs, brain, and other organs        
    leukocidin  class of exotoxin that targets and lyses leukocytes        
    leukocytes  white blood cells of various types, including granulocytes, lymphocytes, and monocytes        
    leukotrienes  lipid-based chemical mediators produced by leukocytes and other tissue cells; promote inflammation and allergic responses        
    lichen  symbiotic association of a fungus with an algae or cyanobacterium        
    ligation  repair of the sugar-phosphate backbone of the DNA, making the DNA molecule continuous        
    light chains  the shorter identical peptide chains of an antibody molecule (two per antibody monomer), composed of variable and constant region segments        
    light-dependent reaction  process by which energy from sunlight is absorbed by pigment molecules in photosynthetic membranes and converted into stored chemical energy in the forms of ATP and NADPH        
    light-harvesting complex  group of multiple proteins and associated pigments that each may absorb light energy to become excited, and transfer this energy from one pigment molecule to another until the energy is delivered to a reaction center pigment        
    light-independent reaction  process by which chemical energy, in the form of ATP and NADPH produced by the light-dependent reactions, is used to fix inorganic CO2 into organic sugar; usually referred to as the Calvin-Benson cycle        
    lincomycin  naturally produced protein synthesis inhibitor of the lincosamide class that binds to the 50S subunit, inhibiting peptide bond formation        
    lincosamides  class of protein synthesis inhibitors that are similar to macrolides        
    linked recognition  a mechanism whereby a B cell and the helper T cell with which it interacts recognize the same antigen        
    lipase  extracellular enzyme that degrades triglycerides        
    lipid bilayer  biological membranes composed of two layers of phospholipid molecules with the nonpolar tails associating to form a hydrophobic barrier between the polar heads; also called unit membrane        
    lipid  macromolecule composed primarily of carbon and hydrogen; source of nutrients for organisms, a storage form for carbon and energy, a part of the structure of membranes, and may function as hormones, pharmaceuticals, fragrances, and pigments        
    lipopolysaccharide (LPS)  lipid molecules with attached sugars that are found as components of gram-negative outer membranes        
    lipoprotein  conjugated protein attached to a lipid        
    listeriosis  bacterial disease caused from the ingestion of the microbe Listeria monocytogenes        
    lithotroph  chemotroph that uses inorganic chemicals as its electron source; also known as chemoautotroph        
    live attenuated vaccine  vaccine with live pathogen that has been attenuated to become less virulent in order to produce an active but subclinical infection        
    liver fluke  a trematode worm that affects the bile duct of the liver, including Fasciola hepatica and F. gigantica        
    local infection  infection in one limited area        
    log phase  interval of growth when cells divide exponentially; also known as the exponential growth phase        
    loiasis  a disease caused by the parasitic Loa loa worm, which is transmitted by deerflies; adult worms live in the subcutaneous tissue and cause inflammation, swelling, and eye pain as they migrate through the skin and the conjunctiva of the eye        
    lophotrichous  having a single tuft of flagella located at one end of a bacterial cell        
    low G+C gram-positive bacteria  bacteria that have less than 50% of guanine and cytosine nucleotides in their DNA        
    lumen  space inside the cisternae of the endoplasmic reticulum in eukaryotic cells        
    Lyme disease  tickborne disease caused by the spirochete Borrelia burgdorferi        
    lymph nodes  bean-shaped organs situated throughout the body that contain areas called germinal centers, which are rich in B and T lymphocytes; also contain macrophages and dendritic cells for antigen presentation        
    lymphadenitis  inflammation of the lymph nodes        
    lymphangitis  inflammation of the lymphatic vessels        
    lymphogranuloma venereum  infection caused by Chlamydia trachomatis in tropical regions        
    lyophilization  rapid freezing, followed by placement under a vacuum, of a material so that water is lost by sublimation, thereby inhibiting microbial growth        
    lysis  destruction of the host cell        
    lysogen  bacterium carrying the prophage        
    lysogenic conversion (phage conversion)  alteration of host characteristics or phenotypes due to the presence of phage        
    lysogenic cycle  life cycle of some phages in which the genome of the infecting phage is integrated into the bacterial chromosome and replicated during bacterial reproduction until it excises and enters a lytic phase of the life cycle        
    lysogeny  process of integrating the phage into the host genome        
    lysosome  an organelle of the endomembrane system that contains digestive enzymes that break down engulfed material such as foodstuffs, infectious particles, or damaged cellular components        
    lytic cycle  infection process that leads to the lysis of host cells        
    M protein  a streptococcal cell wall protein that protects the bacteria from being phagocytized. It is associated with virulence and stimulates a strong immune response        
    macrolides  class of protein synthesis inhibitors containing a large, complex ring structure that binds to the 50S subunit, inhibiting peptide bond formation        
    macromolecule  polymer assembled from of individual units, monomers, that bind together like building blocks        
    macronucleus  larger nucleus in ciliate protists that have two nuclei; polyploid with a reduced genome of metabolic genes and derived from the micronucleus        
    macronutrient  element required in abundance in cells; account for approximately 99% of the cell’s dry weight        
    macrophages  monocytes that have left the bloodstream and differentiated into tissue-specific phagocytes        
    mad cow disease  form of transmissible spongiform encephalopathy primarily affecting cattle; can be transmitted to humans by consumption of contaminated cattle products        
    magnetosomes  inclusions in certain bacterial cells containing magnetic iron oxide or iron sulfide, which allows bacteria to align along a magnetic field by magnetotaxis        
    magnetotaxis  directional movement of bacterial cells using flagella in response to a magnetic field        
    magnification  the power of a microscope (or lens) to produce an image that appears larger than the actual specimen, expressed as a factor of the actual size        
    major histocompatibility complex (MHC)  collection of genes that code for MHC glycoproteins expressed on the surface of all nucleated cells        
    malaise  a general feeling of being unwell        
    malaria  potentially fatal, mosquito-borne protozoan infection caused by several species of Plasmodium and characterized by a relapsing fever, nausea, vomiting, and fatigue        
    mast cells  granulocytes similar in origin and function to basophils, but residing in tissues        
    matrix assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF)  technique in which the sample (e.g., a microbe colony) is mixed with a special matrix and irradiated with a high-energy laser to generate characteristic gaseous ions that are subjected to mass spectral analysis, yielding mass spectra that may be compared to reference data for identification purposes        
    maturation  assembly of viral components to produce a functional virus        
    mature naïve T cell  a T cell that has exited the thymus after thymic selection but has not yet been activated        
    maximum growth pH  highest pH value that an organism can tolerate for growth        
    maximum growth temperature  highest temperature at which a microorganism will divide or survive        
    maximum permissible oxygen concentration  highest concentration of oxygen at which an organism will grow        
    measles  highly contagious respiratory disease caused by the measles virus (MeV); marked by an intense macular rash and high fever; also known as rubeola        
    mebendazole  antihelminthic drug of the benzimidazole class that binds to helminthic β-tubulin, preventing microtubule formation        
    mechanical transmission  transfer of a pathogen between hosts by a mechanical vector        
    mechanical vector  an animal that transfers a pathogen from one host to another or from a reservoir to a host without being infected by the pathogen itself        
    median infectious dose (ID50)  concentration of pathogen that will produce active infection in 50% of test animals inoculated        
    median lethal dose (LD50)  concentration of pathogen that kills 50% of infected test animals        
    medulla  loosely packed layer of fungal filaments located underneath the cortex of a lichen        
    meiosis a two-stage nuclear division process that results in four genetically distinct gametes        
    membrane attack complex (MAC)  ring structure formed from complement proteins C6 through C9 that penetrates the membranes of a targeted cell, causing cell lysis and death        
    membrane filtration  method to remove bacteria from liquid, typically heat-sensitive solutions, using filters with an effective pore size of 0.2 µm or smaller, depending on need        
    membrane filtration technique  known volumes are vacuum filtered aseptically through a membrane with a pore size small enough to trap microorganisms, which are counted after growth on plates        
    membrane-bound ribosome  80S eukaryotic ribosome attached to rough endoplasmic reticulum        
    membrane-disrupting toxin  toxin that affects cell membrane function by either forming pores or disrupting the phospholipid bilayer        
    memory B cell  an activated and differentiated B cell that is programmed to respond to secondary exposures to a specific antigen        
    memory helper T cell  a long-lived T cell programmed to recognize and quickly mount a secondary response to a specific pathogen upon re-exposure        
    memory  the ability of the specific adaptive immune system to quickly respond to pathogens to which it has previously been exposed        
    meninges  membranes that surround the brain        
    meningitis  inflammation of the meningeal membranes that surround the brain        
    meningococcal meningitis  bacterial infection caused by Neisseria meningitidis that results in an inflammation of the meninges        
    meningoencephalitis  inflammatory response that involves both the brain and the membranes that surround it        
    MERS  Middle East respiratory syndrome; first described in Saudi Arabia in 2013; caused by a zoonotic coronavirus that results in flu-like symptoms        
    mesophile  a microorganism that grows best at moderate temperatures, typically between about 20 °C and 45 °C        
    metabolism  all of the chemical reactions inside of cells        
    metachromatic granule  a type of inclusion containing volutin, a polymerized inorganic phosphate that appears red when stained with methylene blue        
    metagenomics  the sequencing of genomic fragments from microbial communities, allowing researchers to study genes from a collection of multiple species        
    metatranscriptomics  the science of studying a collection of mRNA molecules produced from microbial communities; involves studying gene expression patterns from a collection of multiple species        
    methanogen  microorganism that produces gaseous methane        
    methicillin-resistant Staphylococcus aureus (MRSA)  pathogen resistant to all β-lactams through acquisition of a new low-affinity penicillin-binding protein, and often resistant to many other drug classes        
    metronidazole  antibacterial and antiprotozoan drug of the nitroimidazole class that is activated in anaerobic target cell and introduces DNA strand breakage, thus interfering with DNA replication in target cells        
    MHC I molecule  glycoprotein expressed on the surface of all nucleated cells and involved in the presentation of normal “self” antigens and foreign antigens from intracellular pathogens        
    MHC II molecule  glycoprotein expressed only on the surface of antigen-presenting cells and involved in the presentation of foreign antigens from pathogens ingested by phagocytosis        
    micelle  simple spherical arrangement of amphipathic lipid molecules with nonpolar tails aggregated within the interior and polar heads forming the outer surface        
    microaerophile  organism that requires oxygen at levels lower than atmospheric concentration        
    microarray analysis  a technique used to compare two samples of genomic DNA or cDNA; the DNA or cDNA fragments are immobilized on a chip and labeled with different fluorescent dyes, allowing for comparison of sequences or gene-expression patterns        
    microbe  generally, an organism that is too small to be seen without a microscope; also known as a microorganism        
    microbial death curve  graphical representation of the progress of a particular microbial control protocol        
    microbial ecology  study of the interactions between microbial populations microbiology the study of microorganisms        
    microbiome  all prokaryotic and eukaryotic microorganisms and their genetic material that are associated with a certain organism        
    microfilament  cytoskeletal fiber composed of actin filaments        
    microinjection  the direct injection of DNA into the cytoplasm of a eukaryotic cell using a glass micropipette        
    micronucleus  smaller nucleus in ciliate protists that have two nuclei; diploid, somatic, and used for sexual reproduction through conjugation        
    micronutrient  indispensable element present in cells in lower amounts than macronutrients; also called trace element        
    microorganism  generally, an organism that is too small to be seen without a microscope; also known as a microbe        
    microsporidia  fungi that lack mitochondria, centrioles, and peroxisomes; some can be human pathogens        
    microtiter plates  plastic dishes with multiple small wells        
    microtubule  hollow tube composed of tubulin dimers (α and β tubulin); the structural component of the cytoskeleton, centrioles, flagella, and cilia        
    miliary tuberculosis  hematogenous dissemination and spread of Mycobacterium tuberculosis from tubercles        
    minimal bactericidal concentration (MBC)  lowest antibacterial drug concentration that kills ≥99.9% of a starting inoculum of bacteria        
    minimal inhibitory concentration (MIC)  lowest concentration of an antibacterial drug that inhibits visible growth of a bacterial strain        
    minimum growth pH  lowest pH value that an organism can tolerate for growth        
    minimum growth temperature  lowest temperature at which a microorganism will divide or survive        
    minimum permissible oxygen concentration  lowest concentration of oxygen at which an organism will grow        
    missense mutation  point mutation that results in a different amino acid being incorporated into the resulting polypeptide        
    mitochondrial matrix  the innermost space of the mitochondrion enclosed by two membranes; the location of many metabolic enzymes as well as the mitochondrial DNA and 70S ribosomes        
    mitochondrion (plural: mitochondria)  large, complex organelle that is the site of cellular respiration in eukaryotic cells        
    mitosis (also, karyokinesis) period of the cell cycle during which the duplicated chromosomes are separated into identical nuclei; includes prophase, prometaphase, metaphase, anaphase, and telophase        
    mitotic phase period of the cell cycle during which duplicated chromosomes are distributed into two nuclei and cytoplasmic contents are divided; includes karyokinesis (mitosis) and cytokinesis        
    mode of action  way in which a drug affects a microbe at the cellular level        
    moist-heat sterilization  protocol that involves steam under pressure in an autoclave, allowing the steam to reach temperatures higher than the boiling point of water        
    mold  a multicellular fungus, typically made up of long filaments        
    molecular cloning  the purposeful fragmentation of DNA followed by attachment to another piece of DNA to produce a recombinant molecule, followed by introduction of this recombinant molecule into an easily manipulated host to allow for the creation of multiple copies of a gene of interest        
    monoclonal antibodies (mAbs)  antibodies produced in vitro that only bind to a single epitope        
    monocular  having a single eyepiece        
    monocytes  large, agranular, mononuclear leukocytes found in the peripheral blood; responsible for phagocytosis of pathogens and damaged cells        
    monoecious  refers to sexually reproducing organisms in which individuals have both male and female reproductive organs        
    monomer  small organic molecule that binds with like molecules, forming a polymer or macromolecule        
    monosaccharide  monomer for the synthesis of carbohydrate polymers; the simplest carbohydrate, called a simple sugar        
    monotrichous  having one flagellum, typically located on one end of the bacterial cell        
    morbidity  a state of illness        
    Morbidity and Mortality Weekly Report (MMWR)  the trade/industry publication for epidemiologists, reporting US public health data compiled by the CDC        
    morbidity rate  the number of cases of a disease expressed as a percentage of the population or number per standard part of the population, such as 100,000        
    mordant  a chemical added to a specimen that sets a stain        
    mortality  death        
    mortality rate  the number of deaths from a disease expressed as a percentage of the population or number per standard part of the population, such as 100,000        
    most probable number (MPN)  statistical value representing the viable bacterial population in a sample obtained after a series of dilutions and multiple tube inoculations        
    mRNA  short-lived type of RNA that serves as the intermediary between DNA and the synthesis of protein products        
    mucociliary escalator  system by which mucus and debris are propelled up and out of the respiratory tract by the beating of respiratory cilia and the mechanical actions of coughing or swallowing        
    mucormycosis  rare form of pneumonia that can be caused by an invasive infection of different fungi in the order Mucorales, such as Rhizopus or Mucor        
    mucous membrane  moist layer of epithelial cells and interspersed goblet cells that lines the inner surfaces of the body, usually bathed in antimicrobial secretions from the cells of the membrane        
    mucus  viscous secretion produced by cells and glands in various mucous membranes throughout the body; helps trap and remove microbes and debris from the body        
    multidrug-resistant microbes (MDR)  group of pathogens that carry one or more resistance mechanisms, making them resistant to multiple antimicrobials; also called superbugs        
    multidrug-resistant Mycobacterium tuberculosis (MDR-TB)  strains of M. tuberculosis that are resistant to both rifampin and isoniazid, the drug combination typically prescribed for the treatment of tuberculosis        
    multiple sclerosis  autoimmune attack on the myelin sheaths and nerve cells in the central nervous system        
    mumps  a viral illness that causes swelling of the parotid glands; rare in the United States because of effective vaccination        
    murine typhus  fleaborne infection caused by Rickettsia typhi and characterized by fever, rash, and pneumonia        
    mutagen  type of chemical agent or radiation that can induce mutations        
    mutant  organism harboring a mutation that often has a recognizable change in phenotype compared to the wild type        
    mutation  heritable change in the DNA sequence of an organism        
    mutualism  type of symbiosis in which two populations benefit from, and depend on, each other        
    myasthenia gravis  autoimmune disease affecting the acetylcholine receptors in the neuromuscular junction, resulting in weakened muscle contraction capability        
    mycelium  vegetative network of branched, tubular hyphae        
    mycolic acids  waxy molecules associated with peptidoglycan in some gram-positive, acid-fast bacteria, chiefly mycobacteria        
    mycology  the study of fungi        
    Mycoplasma pneumonia  also known as walking pneumonia; a milder form of atypical pneumonia caused by Mycoplasma pneumoniae        
    mycoses, mycosis  refers to diseases caused by fungi        
    mycotoxin  biologically active product of pathogenic fungi that causes adverse changes in the host cells        
    myelin sheath  insulating layer that surrounds the axon of some neurons and helps to promote signal propagation        
    myocarditis  inflammation of the heart muscle tissues        
    naïve mature B cell a B cell that has not yet been activated        
    naked virus virus composed of a nucleic acid core, either DNA or RNA, surrounded by a capsid        
    nalidixic acid member of the quinolone family that functions by inhibiting the activity of DNA gyrase, blocking DNA replication        
    narrow-spectrum antimicrobial drug that targets only a specific subset of microbes        
    nasal cavity air-filled space in the skull immediately behind the nose        
    nasolacrimal duct tear duct connecting the lacrimal glands to the nasal cavity        
    nasopharynx part of the upper throat (pharynx) extending from the posterior nasal cavity; carries air inhaled through the nose        
    native structure three-dimensional structure of folded fully functional proteins        
    natural active immunity immunity that develops as a result of natural infection with a pathogen        
    natural antibiotic antimicrobial compound that is produced naturally by microorganisms in nature        
    natural killer cells (NK cells) lymphoid cells that recognize and destroy abnormal target cells by inducing apoptosis        
    natural passive immunity transfer of maternal antibodies from mother to fetus (transplacentally) or infant (via breastmilk)        
    necrotizing fasciitis a serious infection, also known as flesh-eating disease, that leads to rapid destruction of tissue through the action of exotoxin A; it can be caused by S. pyogenes or several other bacterial species        
    negative (–) single-strand RNA (–ssRNA) a viral RNA strand that cannot be translated until it is replicated into positive single-strand RNA by viral RNA-dependent RNA polymerase        
    negative stain a stain that produces color around the structure of interest while not coloring the structure itself        
    Nematoda phylum comprising roundworms        
    neonatal herpes herpes infection of the newborn, generally caused by infection during birth        
    neonatal meningitis meningitis caused by Group B streptococcus and occurring primarily in neonates (less than 2 months old)        
    neonatal tetanus tetanus acquired through infection of the cut umbilical cord        
    neurocysticercosis parasitic invasion of brain tissues by the larvae of the pork tapeworm, Taenia solium        
    neuromycosis any fungal infection of the nervous system        
    neuron specialized cell found throughout the nervous system that transmits signals through the nervous system using electrochemical processes        
    neuropathy numbness or tingling sensation caused by damage to peripheral nerves        
    neurotoxoplasmosis disease caused by the invasion of brain tissues by the protozoan Toxoplasma gondii; typically only affects immunocompromised patients        
    neurotransmitter compound that is released at the synapse of neurons to stimulate or suppress the actions of other cells        
    neutralism type of symbiosis that does not affect either of the two populations        
    neutralization binding of an antibody to a pathogen or toxin, preventing attachment to target cells        
    neutrophile organism that grows best at a near a neutral pH of 6.5–7.5        
    neutrophils leukocytes with a multilobed nucleus found in large numbers in peripheral blood; able to leave the bloodstream to phagocytose pathogens in infected tissues; also called polymorphonuclear neutrophils (PMNs)        
    next generation sequencing a group of automated techniques used for rapid DNA sequencing        
    nicotine adenine dinucleotide (NAD+/NADH) oxidized/reduced forms of an electron carrier in cells        
    nicotine adenine dinucleotide phosphate (NADP+/NADPH) oxidized/reduced forms of an electron carrier in cells        
    nitrogen fixation bacterial biochemical pathways that incorporate inorganic nitrogen gas into organic forms more easily used by other organisms        
    nitrogenous base nitrogen-containing ring structure within a nucleotide that is responsible for complementary base pairing between nucleic acid strands        
    noncoding DNA regions of an organism’s genome that, unlike genes, do not encode proteins        
    noncommunicable disease disease that is not transmitted from one person to another        
    noncompetitive (allosteric) inhibitor molecule that binds to allosteric sites, inducing a conformational change in the enzyme’s structure that prevents it from functioning        
    noncritical item object that may contact intact skin but does not penetrate it; requires cleanliness but not a high level of disinfection        
    noncyclic photophosphorylation pathway used in photosynthetic organisms when both ATP and NADPH are required by the cell        
    nonenveloped virus naked virus        
    nongonococcal urethritis (NGU) a nonspecific infection of the urethra that is not caused by Neisseria gonorrhoeae        
    noninfectious disease disease caused by something other than an infectious agent (e.g., genetics, environment, nutritional deficiencies)        
    nonionizing radiation low-energy radiation, like ultraviolet light, that can induce dimer formation between two adjacent pyrimidine bases, resulting in DNA polymerase stalling and possible formation of a frameshift mutation        
    nonsense mutation point mutation that converts a codon encoding an amino acid (a sense codon) into a stop codon (a nonsense codon)        
    nontreponemal serologic tests qualitative and quantitative indirect diagnostic tests for syphilis        
    northern blot a technique in molecular genetics used to detect the amount of RNA made by gene expression within a tissue or organism sample; RNA fragments within a sample are separated by agarose gel electrophoresis, immobilized on a membrane, and then exposed to a specific DNA probe labeled with a radioactive or fluorescent molecular beacon to aid in detection        
    nosocomial disease disease acquired in a hospital setting        
    notifiable disease a disease for which all cases must legally be reported to regional, state, and/or federal public health agencies        
    nuclear envelope (also called the nuclear membrane) a structure defining the boundary of the nucleus; composed of two distinct lipid bilayers that are contiguous with each other and with the endoplasmic reticulum        
    nuclear lamina a meshwork of intermediate filaments (mainly lamins) found just inside the nuclear envelope; provides structural support to the nucleus        
    nucleic acid class of macromolecules composed of nucleotide monomers polymerized into strands        
    nucleoid concentrated area of DNA genome and associated proteins found in a prokaryotic cell that is not surrounded by a membrane        
    nucleoid-associated protein (NAP) protein that assists in the organization and packaging of the chromosome in prokaryotic cells        
    nucleolus a dense region within the nucleus where ribosomal RNA biosynthesis occurs and preribosomal complexes are made        
    nucleoside analog, nucleoside analogs chemical that is structurally similar to a normal nucleotide base that can be incorporated into DNA instead of normal bases during replication but that has different base pairing rules than the normal base for which it was substituted, inducing mutation        
    nucleotide excision repair (dark repair) enzymatic mechanism to repair pyrimidine dimers by cutting the dimer-containing DNA strand on both sides of dimer, removing the intervening strand and replacing the bases with the correct ones        
    nucleotide nucleic acid monomer composed of a pentose sugar, a phosphate group, and a nitrogenous base        
    nucleus a membrane-bound structure of eukaryotic cells that houses the DNA genome        
    numerical aperture a measure of a lens’s ability to gather light        
    objective lenses on a light microscope, the lenses closest to the specimen, typically located at the ends of turrets        
    obligate aerobe organism that requires oxygen for growth        
    obligate anaerobe organism that dies in the presence of oxygen        
    obligate intracellular pathogen microorganism that cannot synthesize its own ATP and, therefore, must rely on a host cell for energy; behaves like a parasite when inside a host cell, but is metabolically inactive outside of a host cell        
    observational study a type of scientific study that involves measurement of study subjects on variables hypothesized to be associated with the outcome of interest, but without any manipulation of the subjects        
    ocular lens on a microscope, the lens closest to the eye (also called an eyepiece)        
    oil immersion lens a special objective lens on a microscope designed to be used with immersion oil to improve resolution        
    Okazaki fragment short fragment of DNA made during lagging strand synthesis        
    oligopeptide peptide having up to approximately 20 amino acids        
    opacity the property of absorbing or blocking light        
    operator DNA sequence located between the promoter region and the first coding gene to which a repressor protein can bind        
    operon a group of genes with related functions often found clustered together within the prokaryotic chromosome and transcribed under the control of a single promoter and operator repression sequence        
    ophthalmia neonatorum inflammation of the conjunctiva in newborns caused by Neisseria gonorrhoeae transmitted during childbirth        
    opisthotonos characteristic symptom of tetanus that results in uncontrolled muscular spasms and backward arching of the neck and spine        
    opportunistic pathogen microorganism that can cause disease in individuals with compromised host defenses        
    opsonin any molecule that binds to and coats the outside of a pathogen, identifying it for destruction by phagocytes (examples include antibodies and the complement proteins C3b and C4b)        
    opsonization process of coating a pathogen with a chemical substance (an opsonin) that allows phagocytic cells to recognize, engulf, and destroy the pathogen more easily        
    optimum growth pH the pH at which an organism grows best        
    optimum growth temperature the temperature at which a microorganism’s growth rate is highest        
    optimum oxygen concentration the ideal concentration of oxygen for a particular microorganism        
    oral herpes an infection caused by herpes simplex virus that results in cold sores, most commonly on and around the lips        
    oral thrush Candida infection of the mouth        
    orchitis inflammation of one or both of the testes        
    organic molecule composed primarily of carbon; typically contains at least one carbon atom bound to one or more hydrogen atoms        
    organotroph chemotroph that uses organic molecules as its electron source; also known as chemoheterotroph        
    origin of replication specific nucleotide sequence where replication begins        
    oropharynx area where air entering mouth enters the pharynx        
    osmosis diffusion of water across a semipermeable membrane        
    osmotic pressure the force or pressure generated by water diffusing across a semipermeable membrane, driven by differences in solute concentration across the membrane        
    osteomyelitis inflammation of bone tissue        
    otitis externa an infection of the external ear canal, most commonly caused by Pseudomonas aeruginosa; often called swimmer’s ear        
    otitis inflammation of the ear        
    otitis media with effusion accumulation of fluid inside the middle ear with or without infection        
    Ouchterlony assay test in which antigen and antisera are added to neighboring wells in an agar gel, allowing visualization of precipitin arcs        
    outer membrane a phospholipid bilayer external to the peptidoglycan layer found in gram-negative cell walls        
    oxazolidinones class of synthetic protein synthesis inhibitors that interfere with formation of the initiation complex for translation and prevent translocation of the growing protein from the ribosomal A site to the P site        
    oxidation reaction chemical reaction that removes electrons (often as part of H atoms) from donor molecules, leaving them oxidized        
    oxidative phosphorylation mechanism for making ATP that uses the potential energy stored within an electrochemical gradient to add Pi to ADP        
    oxygenic photosynthesis type of photosynthesis found in plants, algae, and cyanobacteria, and in which H2O is used as the electron donor to replace an electron lost by a reaction center pigment, resulting in oxygen as a byproduct        
    P (peptidyl) site functional site of an intact ribosome that binds charged tRNAs carrying amino acids that have formed peptide bonds with the growing polypeptide chain but have not yet dissociated from their corresponding tRNA        
    palatine tonsil lymphoid tissue located near the oropharynx        
    pandemic disease an epidemic that is worldwide as opposed to regional        
    papilloma growth on the skin associated with infection by any of the human papilloma viruses (HPV); commonly known as a wart        
    paracrine function refers to a cytokine signal released from a cell to a receptor on a nearby cell        
    parasitism type of symbiosis in which one population benefits while harming the other parasitology the study of parasites        
    parenteral route means of entry by a pathogen through skin or mucous membranes when these barriers are breached        
    paroxysmal stage most serious stage of pertussis (whooping cough), characterized by severe and prolonged coughing spells        
    passive carrier an individual capable of transmitting a pathogen to another individual without becoming infected        
    passive immunity adaptive immune defenses received from another individual or animal        
    pasteurization form of microbial control using heat that is applied to foods; kills pathogens and reduces the number of spoilage-causing microbes while maintaining food quality        
    pathogen a disease-causing microorganism        
    pathogen-associated molecular patterns (PAMPs) common molecular motifs found on pathogens        
    pathogenicity ability of a microbial agent to cause disease        
    pattern recognition receptors (PRRs) receptors on the surface or in the interior of phagocytic cells that bind to pathogen-associated molecular patterns (PAMPs)        
    pellicle structure that underlies the plasma membrane in protists, providing additional support        
    pelvic inflammatory disease (PID) infection of the female reproductive organs that may spread from the vagina to the cervix, uterus, fallopian tubes, and ovaries        
    penetration entry of phage or virus into a host cell through injection, endocytosis, or membrane fusion        
    penicillin β-lactam antibacterial that was the first cell wall synthesis inhibitor developed        
    penis external genital organ in males through which urine and semen are discharged        
    pentamidine antiprotozoan drug that appears to degrade kDNA in target cells, as well as inhibit protein synthesis        
    pentose phosphate pathway (PPP) alternative glycolytic pathway that produces intermediates used for the biosynthesis of nucleotides and amino acids; also called the phosphogluconate pathway or the hexose monophosphate shunt        
    peptic ulcer an ulcer in the lining of the stomach or duodenum, often associated with Helicobacter pylori        
    peptide bond bond between the carboxyl group of one amino acid and the amine group of another; formed with the loss of a water molecule        
    peptidoglycan (murein) the polymer of alternating N-acetylmuramic acid NAM and N-acetylglucosamine (NAG) subunits linked together by peptide chains; a major constituent of bacterial cell walls        
    peptidyl transferase RNA-based ribozyme that is part of the 50S ribosomal subunit and catalyzes formation of the peptide bond between the amino acid bound to a tRNA and the growing polypeptide chain        
    perforin compound released from a natural killer cell that creates pores in the target cell through which other toxins (particularly granzymes) can gain access to the cytoplasm        
    pericarditis inflammation of the sac that surrounds the heart        
    period of convalescence fifth stage of acute disease, during which the patient returns to normal function        
    period of decline fourth stage of disease, during which the number of pathogens present in the host decreases, along with signs and symptoms of disease        
    period of illness third stage of acute disease, during which the number of pathogens present in the host is greatest and the signs and symptoms of disease are most severe        
    periodontal disease a condition in which the gums are inflamed and may erode        
    periodontitis inflammation of the gums that is more severe than gingivitis, spreading deeper into the tissues        
    peripheral nervous system network of neurons that connects the CNS with organs, sensory organs, and muscles throughout the body        
    peripheral tolerance mechanism by which regulatory T cells inhibit self-reactive immune responses in T cells that have already exited the thymus        
    periplasmic space the space between the cell wall and the plasma membrane, primarily in gram-negative bacteria        
    peristalsis muscular contractions of the gastrointestinal tract that propel ingested material through the stomach, intestines, and, eventually, through the rectum and out of the body        
    peritrichous having numerous flagella covering the entire surface of a bacterial cell        
    peroxidase enzyme that catalyzes the detoxification of peroxides        
    peroxisome in eukaryotic cells, a membrane-bound organelle (not part of the endomembrane system) that produces hydrogen peroxide to break down various types of molecules; also plays a role in lipid biosynthesis        
    peroxygen type of strong oxidizing agent that causes free radical formation in cells; can be used as a disinfectant or antiseptic        
    persister dormant cell that survives in the death phase and is resistant to most antibiotics        
    pertussis contagious illness caused by Bordetella pertussis that causes severe coughing fits followed by a whooping sound during inhalation; commonly known as whooping cough        
    pertussis toxin main virulence factor accounting for the symptoms of whooping cough        
    petechiae small red or purple spots on the skin that result from blood leaking out of damaged vessels        
    Petroff-Hausser counting chamber calibrated slide that allows counting of bacteria in a specific volume under a microscope        
    Peyer’s patches lymphoid tissue in the ileum that monitors and fights infections        
    phagemid a plasmid capable of being replicated as a plasmid and also incorporated into a phage head        
    phagocytosis a type of endocytosis in which large particles are engulfed by membrane invagination, after which the particles are enclosed in a pocket, which is pinched off from the membrane to form a vacuole        
    phagolysosome compartment in a phagocytic cell that results when the phagosome is fused with the lysosome, leading to the destruction of the pathogens inside        
    phagosome compartment in the cytoplasm of a phagocytic cell that contains the phagocytosed pathogen enclosed by part of the cell membrane        
    pharmacogenomics (toxicogenomics) the evaluation of the effectiveness and safety of drugs on the basis of information from an individual’s genomic sequence as well as examination of changes in gene expression in response to the drug        
    pharyngitis inflammation of the pharynx        
    pharynx region connecting the nose and mouth to the larynx: the throat        
    phase-contrast microscope a light microscope that uses an annular stop and annular plate to increase contrast        
    phenol coefficient measure of the effectiveness of a chemical agent through comparison with that of phenol on Staphylococcus aureus and Salmonella enterica serovar Typhi        
    phenolics class of chemical disinfectants and antiseptics characterized by a phenol group that denatures proteins and disrupts membranes        
    phenotype observable characteristics of a cell or organism        
    phosphodiester bonds linkage whereby the phosphate group attached to the 5ʹ carbon of the sugar of one nucleotide bonds to the hydroxyl group of the 3ʹ carbon of the sugar of the next nucleotide        
    phosphogluconate pathway see pentose phosphate pathway        
    phospholipase enzyme that degrades phospholipids        
    phospholipid complex lipid that contains a phosphate group        
    phospholipid-derived fatty acids (PLFA) analysis technique in which membrane phospholipids are saponified to release the fatty acids of the phospholipids, which can be subjected to FAME analysis for identification purposes        
    phosphorescence the ability of certain materials to absorb energy and then release that energy as light after a delay        
    photosynthesis process whereby phototrophic organisms convert solar energy into chemical energy that can then be used to build carbohydrates        
    photosynthetic pigment pigment molecule used by a cell to absorb solar energy; each one appears the color of light that it transmits or reflects        
    photosystem organized unit of pigments found within a photosynthetic membrane, containing both a light-harvesting complex and a reaction center        
    phototaxis directional movement using flagella in response to light        
    phototroph organism that gets its energy from light        
    phototrophic bacteria nontaxonomic group of bacteria that use sunlight as their primary source of energy        
    phylogeny the evolutionary history of a group of organisms        
    phytoplankton photosynthetic plankton        
    pia mater fragile and innermost membrane layer surrounding the brain        
    pili long protein extensions on the surface of some bacterial cells; specialized F or sex pilus aids in DNA transfer between cells        
    pinocytosis a type of endocytosis in which small dissolved materials are endocytosed into smaller vesicles        
    plague infectious epidemic disease caused by Yersinia pestis        
    plankton microscopic organisms that float in the water and are carried by currents; they may be autotrophic (phytoplankton) or heterotrophic (zooplankton)        
    planktonic free-floating or drifting in suspension        
    plantibodies monoclonal antibodies produced in plants that are genetically engineered to express mouse or human antibodies        
    plaque clear area on bacterial lawn caused by viral lysis of host cells        
    plasma cell activated and differentiated B cell that produces and secretes antibodies        
    plasma fluid portion of the blood that contains all clotting factors        
    plasma membrane (also called the cell membrane or cytoplasmic membrane) lipid bilayer with embedded proteins that defines the boundary of the cell        
    plasmalemma protist plasma membrane        
    plasmid small, circular, double-stranded DNA molecule that is typically independent from the bacterial chromosome        
    plasmolysis the separation of the plasma membrane away from the cell wall when a cell is exposed to a hypertonic environment        
    platelets cell fragments in the peripheral blood that originate from megakaryocyte cells in the bone marrow; also called thrombocytes        
    Platyhelminthes phylum comprising flatworms        
    pleconaril an antiviral drug targeting picornaviruses that prevents the uncoating of virus particles upon their infection of host cells        
    pleomorphic able to change shape        
    pneumococcal meningitis bacterial infection caused by Streptococcus pneumoniae that results in an inflammation of the meninges        
    Pneumocystis pneumonia common pulmonary infection in patients with AIDS; caused by P. jirovecii        
    pneumonia pulmonary inflammation that causes the lungs to fill with fluids        
    pneumonic plague rare form of plague that causes massive hemorrhages in the lungs and is communicable through aerosols        
    point mutation mutation, most commonly a base substitution, that affects a single base pair        
    point source spread a form of common source spread in which the transmission of a disease from the source occurs for a brief period that is less than the pathogen’s incubation period        
    polar tubule a tube-like structure produced by spores of parasitic Microsporidia fungi that pierces host cell membranes        
    poliomyelitis (polio) disease caused by an infection of the enteric polio virus characterized by inflammation of the motor neurons of the brain stem and spinal cord; can result in paralysis        
    poly-A tail string of approximately 200 adenine nucleotides added to the 3’ end of a eukaryotic primary mRNA transcript to stabilize it        
    polyacrylamide gel electrophoresis (PAGE) a method for separating populations of proteins and DNA fragments during Sanger sequencing of varying sizes by differential migration rates caused by a voltage gradient through a vertical gel matrix        
    polycistronic mRNA single mRNA molecule commonly produced during prokaryotic transcription that carries information encoding multiple polypeptides        
    polyclonal antibodies antibodies produced in a normal immune response, in which multiple clones of B cells respond to many different epitopes on an antigen        
    polyenes class of antifungal drugs that bind to ergosterol to form membrane pores, disrupting fungal cell membrane integrity        
    polyhedral virus virus with a three-dimensional shape with many facets        
    polyhydroxybutyrate (PHB) a type of cellular inclusion surrounded by a phospholipid monolayer embedded with protein        
    polylinker site or multiple cloning site (MCS) a short sequence containing multiple unique restriction enzyme recognition sites that are used for inserting foreign DNA into the plasmid after restriction digestion of both the foreign DNA and the plasmid        
    polymer macromolecule composed of individual units, monomers, that bind together like building blocks.        
    polymerase chain reaction (PCR) an in vitro molecular technique that rapidly amplifies the number of copies of specific DNA sequences to make the amplified DNA available for other analyses        
    polymorphonuclear neutrophil (PMN) see neutrophils        
    polymyxins lipophilic polypeptide antibiotics that target the lipopolysaccharide component of gram-negative bacteria and ultimately disrupt the integrity of their outer and inner membranes        
    polypeptide polymer having from approximately 20 to 50 amino acids        
    polyphyletic refers to a grouping of organisms that is not descended from a single common ancestor        
    polyribosome (polysome) structure including an mRNA molecule that is being translated by multiple ribosomes concurrently        
    polysaccharide polymer composed of hundreds of monosaccharides linked together by glycosidic bonds; also called glycans        
    portal of entry anatomical feature of the body through which pathogens can enter host tissue        
    portal of exit anatomical feature of the body through which pathogens can leave diseased individual        
    positive (+) strand viral RNA strand that acts like messenger RNA and can be directly translated inside the host cell        
    positive stain a stain that colors the structure of interest        
    pour plate method a technique used for inoculating plates with diluted bacterial samples for the purpose of cell counting; cells are mixed with warm liquid agar before being poured into Petri dishes        
    praziquantel antihelminthic drug that induces a calcium influx into tapeworms, leading to spasm and paralysis        
    precipitin complex lattice of antibody and antigen that becomes too large to stay in solution        
    precipitin ring test assay in which layers of antisera and antigen in a test tube form precipitin at the interface of the two solutions        
    prevalence the total number or proportion of individuals in a population ill with a specific disease        
    primary amoebic meningoencephalitis (PAM) acute and deadly parasitic infection of brain tissues by the amoeba Naegleria fowleri        
    primary antibody in a sandwich ELISA, the antibody that is attached to wells of a microtiter plate to capture antigen from a solution, or in an indirect ELISA, the antigen-specific antibody present in a patient’s serum        
    primary cell culture cells taken directly from an animal or plant and cultured in vitro        
    primary immunodeficiency genetic condition that results in impaired immune function        
    primary infection initial infection produced by a pathogen        
    primary lymphoid tissue one of two types of lymphatic tissue; comprises bone marrow and the thymus        
    primary pathogen microorganism that can cause disease in the host regardless of the effectiveness of the host’s immune system        
    primary response the adaptive immune response produced upon first exposure to a specific antigen        
    primary stain refers, in differential staining techniques, to the first dye added to the specimen        
    primary structure bonding sequence of amino acids in a polypeptide chain protein macromolecule that results when the number of amino acids linked together becomes very large, or when multiple polypeptides are used as building subunits        
    primary transcript RNA molecule directly synthesized by RNA polymerase in eukaryotes before undergoing the additional processing required to become a mature mRNA molecule        
    primase RNA polymerase enzyme that synthesizes the RNA primer required to initiate DNA synthesis        
    primer short complementary sequence of five to 10 RNA nucleotides synthesized on the template strand by primase that provides a free 3’-OH group to which DNA polymerase can add DNA nucleotides        
    prion acellular infectious particle consisting of just proteins that can cause progressive diseases in animals and humans        
    prodromal period second stage of acute disease, during which the pathogen continues to multiply in the host and nonspecific signs and symptoms become observable        
    progeny virus newly assembled virions ready for release outside the cell        
    proglottid body segment of a cestode (tapeworm)        
    prokaryote an organism whose cell structure does not include a membrane-bound nucleus        
    prokaryotic cell a cell lacking a nucleus bound by a complex nuclear membrane        
    promoter DNA sequence onto which the transcription machinery binds to initiate transcription        
    propagated spread the progression of an infectious disease from person to person, either indirectly or directly, through a population of susceptible individuals as one infected individual transmits the agent to others, who transmit it to others yet again        
    prophage phage genome that has incorporated into the host genome        
    prospective study a research design that follows cases from the beginning of the study through time to associate measured variables with outcomes        
    prostate gland gland that contributes fluid to semen        
    prostatitis inflammation of the prostate gland        
    protease enzyme involved in protein catabolism that removes individual amino acids from the ends of peptide chains        
    protease inhibitor class of antiviral drugs, used in HIV therapy and hepatitis C therapy, that inhibits viral-specific proteases, preventing viral maturation        
    protein signature an array of proteins expressed by a cell or tissue under a specific condition        
    Proteobacteria phylum of gram-negative bacteria        
    proteomic analysis study of all accumulated proteins of an organism        
    proteomics the study of the entire complement of proteins in an organism; involves monitoring differences in gene expression patterns between cells at the protein level        
    protists informal name for diverse group of eukaryotic organisms, including unicellular, colonial, and multicellular types that lack specialized tissues        
    proton motive force electrochemical gradient formed by the accumulation of hydrogen ions (also known as protons) on one side of a membrane relative to the other        
    protozoan (plural: protozoa), protozoan, protozoa a unicellular eukaryotic organism, usually motile        
    protozoans informal term for some protists, generally those that are nonphotosynthetic, unicellular, and motile protozoology the study of protozoa        
    provirus animal virus genome that has integrated into the host chromosome        
    pseudohyphae short chains of yeast cells stuck together        
    pseudomembrane grayish layer of dead cells, pus, fibrin, red blood cells, and bacteria that forms on mucous membranes of the nasal cavity, tonsils, pharynx, and larynx of individuals with diphtheria        
    pseudomembranous colitis inflammation of the large intestine with the formation of a pseudomembrane; caused by C. difficile        
    pseudopodia temporary projections involved in ameboid movement; these “false feet” form by gel-sol cycling of actin polymerization/depolymerization        
    psittacosis zoonotic Chlamydophila infection from birds that causes a rare form of pneumonia        
    psoriasis autoimmune disease involving inflammatory reactions in and thickening of skin        
    psychrophile a microorganism that grows best at cold temperatures; most have an optimum growth temperature of about 15 °C and can survive temperatures below 0 °C; most cannot survive temperatures above 20 °C        
    psychrotroph a microorganism that grows best at cool temperatures, typically between about 4 °C and 25 °C, with optimum growth at about 20 °C        
    puerperal sepsis sepsis associated with a bacterial infection incurred by a woman during or after childbirth        
    purines nitrogenous bases containing a double-ring structure with a six-carbon ring fused to a five-carbon ring; includes adenine and guanine        
    purple nonsulfur bacteria phototrophic bacteria that are similar to purple sulfur bacteria except they use hydrogen rather than hydrogen sulfide for oxidation        
    purple sulfur bacteria phototrophic bacteria that oxidize hydrogen sulfide into elemental sulfur and sulfuric acid; their purple color is due to the pigments bacteriochlorophylls and carotenoids        
    purulent an infection that produces pus; suppurative        
    pus accumulation of dead pathogens, neutrophils, tissue fluid, and other bystander cells that may have been killed by phagocytes at the site of an infection        
    pyelonephritis an infection of one or both kidneys        
    pyocyanin blue pigments produced by some strains of Pseudomonas aeruginosa        
    pyoderma any suppurative (pus-producing) infection of the skin        
    pyoverdin a water-soluble, yellow-green or yellow-brown pigment produced by some strains of Pseudomonas aeruginosa        
    pyrimidines nitrogenous bases containing a single six-carbon ring; includes cytosine and thymine in DNA        
    pyrophosphate (PPi) two connected phosphate groups in solution        
    pyuria pus or white blood cells in the urine        
    Q fever highly infectious zoonotic disease caused by Coxiella burnetii that farmers can contract from their animals by inhalation        
    quarantine the isolation of an individual for the purpose of preventing the spread of disease        
    quaternary ammonium salts (quats) group of cationic detergents, named for the characteristic quaternary nitrogen atom that confers a positive charge, that make up an important class of disinfectants and antiseptics        
    quaternary structure structure of protein complexes formed by the combination of several separate polypeptides or subunits        
    quinolines class of antiprotozoan drugs long used for the treatment of malaria; interferes with heme detoxification        
    quorum sensing cell-to-cell communication in bacteria; enables a coordinated response from cells when the population reaches a threshold density        
    R plasmid plasmid containing genes encoding proteins that make a bacterial cell resistant to one or more antibiotics        
    rabies contagious viral disease primarily transmitted by the bite of infected mammals that can cause acute encephalitis resulting in madness, aggressiveness, coma, and death        
    radial immunodiffusion precipitin reaction in which antigen added to a well in an antiserum-impregnated gel diffuses, producing a precipitin ring whose diameter squared is directly proportional to antigen concentration        
    rat-bite fever relapsing fever caused by either Bacillus moniliformis or Spirillum minor; can be transmitted by the bite of a rat or through contact with rat feces or urine        
    reaction center protein complex in a photosystem, containing a pigment molecule that can undergo oxidation upon excitation by a light-harvesting pigment, actually giving up an electron        
    reactivation tuberculosis secondary infection by Mycobacterium tuberculosis that forms later in life; occurs when the bacteria escape from the Ghon complexes and establish focal infections at other sites in immunocompromised individuals        
    reactive oxygen species (ROS) unstable and toxic ions and molecules derived from partial reduction of oxygen        
    reading frame way nucleotides in mRNA are grouped into codons        
    real-time PCR, quantitative PCR, qPCR a variant of PCR involving the use of fluorescence to allow for the monitoring of the increase in double-stranded template during a PCR reaction as it occurs, allowing for the quantitation of the original target sequence        
    receptor-mediated endocytosis a type of endocytosis in which extracellular ligands are targeted to specific cells through their binding to specific cell surface receptors        
    recognition site a specific, often palindromic, DNA sequence recognized by a restriction enzyme that is typically four to six base pairs long and reads the same in the 5ʹ to 3ʹ direction on one strand as it does in the 5ʹ to 3ʹ direction on the complementary strand        
    recombinant DNA molecule a DNA molecule resulting from the cutting and insertion of DNA from one organism into the DNA of another organism, resulting in a new combination of genetic material        
    recombinant DNA pharmaceuticals pharmaceuticals produced as a result of genetic engineering        
    recombinant DNA technology the process by which DNA from one organism is cut and new pieces of foreign DNA from a second organism are inserted, artificially creating new combinations of genetic material within the organism        
    redox potential tendency for a molecule to acquire electrons and become reduced; electrons flow from molecules with lower redox potentials to those with higher redox potentials        
    redox reaction pairing of an oxidation reaction with a reduction reaction        
    reduction reaction chemical reaction that adds electrons to acceptor molecules, leaving them reduced        
    reemerging infectious disease a disease that was once under control or largely eradicated that has begun causing new outbreaks due to changes in susceptible populations, the environment, or the pathogen itself        
    reflection when light bounces back from a surface        
    refraction bending of light waves, which occurs when a light wave passes from one medium to another        
    refractive index a measure of the magnitude of slowing of light waves by a particular medium        
    regulatory T cells class of T cells that are activated by self-antigens and serve to inhibit peripheral self-reacting T cells from causing damage and autoimmunity        
    rejection process by which adaptive immune responses recognize transplanted tissue as non-self, mounting a response that destroys the tissue or leads to the death of the individual        
    relapsing fever louse- or tickborne disease caused by Borrelia recurrentis or B. hermsii and characterized by a recurrent fever        
    replica plating plating technique in which cells from colonies growing on a complete medium are inoculated onto various types of minimal media using a piece of sterile velvet, ensuring that the orientation of cells deposited on all plates is the same so that growth (or absence thereof) can be compared between plates        
    replication bubble circular structure formed when the DNA strands are separated for replication        
    replication fork Y-shaped structure that forms during the process of replication as DNA unwinds and opens up to separate the DNA strands        
    replication process by which DNA is copied        
    reporter genes genes that encode easily observable characteristics, allowing for their expression to be easily monitored        
    repressible operon bacterial operon, that typically containing genes encoding enzymes required for a biosynthetic pathway and that is expressed when the product of the pathway continues to be required but is repressed when the product of the pathway accumulates, removing the need for continued expression        
    repressor protein that suppresses transcription of a gene or operon in response to an external stimulus        
    reservoir a living host or nonliving site in which a pathogenic organism can survive or multiply        
    resident microbiota microorganisms that constantly live in the human body        
    resolution the ability to distinguish between two points in an image        
    restriction endonuclease (restriction enzyme) bacterial enzyme that cuts DNA fragments at a unique, often palindromic, recognition site; used in genetic engineering for splicing DNA fragments together into recombinant molecules        
    restriction fragment length polymorphism (RFLP) a genetic variant identified by differing numbers or sizes of DNA fragments generated after digestion of a DNA sample with a restriction endonuclease; the variants are caused by the loss or gain of restriction sites, or the insertion or deleting of sequences between restriction sites.        
    retort large industrial autoclave used for moist heat sterilization on a large scale        
    retrospective study a research design that associates historical data with present cases        
    retrovirus positive ssRNA virus that produces and uses reverse transcriptase to make an ssDNA copy of the retroviral genome that can then be made into dsDNA and integrate into the host cell chromosome to form a provirus within the host chromosome.        
    reverse transcriptase enzyme found in retroviruses that can make a copy of ssDNA from ssRNA        
    reverse transcriptase inhibitor classes of antiviral drugs that involve nucleoside analog competitive inhibition and non-nucleoside noncompetitive inhibition of the HIV reverse transcriptase        
    reverse transcriptase PCR (RT-PCR) a variation of PCR used to obtain DNA copies of a specific mRNA molecule that begins with the conversion of mRNA molecules to cDNA by the enzyme reverse transcriptase        
    Reye syndrome potentially life-threatening sequelae to some viral infections that result in the swelling of the liver and brain; aspirin use has also been linked to this syndrome        
    Rh factor red blood cell surface antigen that can trigger type II hypersensitivity reactions        
    rheostat a dimmer switch that controls the intensity of the illuminator on a light microscope        
    rheumatic fever serious clinical sequela of an infection with Streptococcus pyogenes that can result in damage to joints or the valves of the heart        
    rheumatoid arthritis systemic autoimmune disease in which immune complexes form and deposit in the joints and their linings, leading to inflammation and destruction        
    rhinitis inflammation of the nasal cavity        
    rhizines structures made of hyphae found on some lichens; aid in attachment to a surface        
    ribonucleic acid (RNA) single-stranded nucleic acid composed of ribonucleotides; important in transcription and translation (protein synthesis)        
    ribonucleotides RNA nucleotides containing ribose as the pentose sugar component and a nitrogenous base        
    ribosome a complex intracellular structure that synthesizes proteins        
    riboswitch small region of noncoding RNA found within the 5’ end of some prokaryotic mRNA molecules that may bind to a small intracellular molecule, influencing the completion of transcription and/or translation        
    ribulose bisphosphate carboxylase (RuBisCO) first enzyme of the Calvin cycle responsible for adding a CO2 molecule onto a five-carbon ribulose bisphosphate (RuBP) molecule        
    rifampin semisynthetic member of the rifamycin class that blocks bacterial RNA polymerase activity, inhibiting transcription        
    rimantadine antiviral drug that targets the influenza virus by preventing viral escape from endosomes upon host cell uptake, preventing viral RNA release and subsequent viral replication        
    ringworm a tinea (cutaneous mycosis of the skin), typically characterized by a round, red, slightly raised lesion that heals outward from the center, giving it the appearance of a round worm        
    RNA interference (RNAi) process by which antisense RNAs or small interfering RNAs (siRNAs) interfere with gene expression by binding to mRNA, preventing translation and protein synthesis        
    RNA polymerase enzyme that adds nucleotides to the 3’-OH group of the growing mRNA molecule that are complementary to the template strand, forming covalent phosphodiester bonds between the nucleotides in the RNA        
    RNA splicing process of removing intron-encoded RNA sequences from eukaryotic primary transcripts and reconnecting those encoded by exons        
    RNA transcript mRNA produced during transcription        
    Rocky Mountain spotted fever potentially fatal tickborne disease caused by Rickettsia rickettsii characterized by fever, body aches, and a rash        
    rogue form misfolded form of the PrP protein that is normally found in the cell membrane and has the tendency to aggregate in neurons, causing extensive cell death and brain damage        
    rolling circle replication type of rapid unidirectional DNA synthesis of a circular DNA molecule        
    roseola a rash-causing illness, most commonly affecting children, associated with human herpesvirus 6 (HHV-6)        
    rough endoplasmic reticulum a type of endoplasmic reticulum containing bound 80S ribosomes for the synthesis of proteins destined for the plasma membrane        
    route of administration method used to introduce a drug into the body        
    rRNA type of stable RNA that is a major constituent of ribosomes, ensuring proper alignment of the mRNA and the ribosomes as well as catalyzing the formation of the peptide bonds between two aligned amino acids during protein synthesis        
    rubella German measles, caused by the rubella virus        
    runs (running) purposeful, directional movement of a prokaryotic cell propelled by counterclockwise flagellar rotation        
    σ factor subunit of bacterial RNA polymerase conferring promoter specificity that can be substituted with a different version in response to an environmental condition, allowing for a quick and global change of the regulon transcribed        
    saccharide carbohydrate        
    salmonellosis gastrointestinal illness caused by Salmonella bacteria        
    salpingitis inflammation of the fallopian tubes        
    sandwich ELISA EIA in which the primary antibody is first attached to the wells of a microtiter plate, allowing it to capture antigen from an unknown solution to be quantified        
    Sanger DNA sequencing, dideoxy method, chain termination method the original DNA sequencing technique in which dideoxy nucleotides, each labeled with a molecular beacon, are used to terminate chain elongation; the resulting incrementally sized fragments are then separated by electrophoresis to determine the sequence of the DNA molecule        
    sanitization protocol that reduces microbial load on inanimate surfaces to levels deemed safe for public health        
    saprozoic refers to protozoans that ingest small, soluble food molecules        
    SARS severe acute respiratory syndrome; caused by a zoonotic coronavirus that results in flu-like symptoms        
    saturated fatty acid lipid with hydrocarbon chains containing only single bonds, which results in the maximum number of hydrogen atoms per chain        
    scanning electron microscope (SEM) a type of electron microscope that bounces electrons off of the specimen, forming an image of the surface        
    scanning probe microscope a microscope that uses a probe that travels across the surface of a specimen at a constant distance while the current, which is sensitive to the size of the gap, is measured        
    scanning tunneling microscope a microscope that uses a probe that is passed just above the specimen as a constant voltage bias creates the potential for an electric current between the probe and the specimen        
    scarlet fever bacterial infection caused by Streptococcus pyogenes, marked by a high fever and a disseminated scarlet rash        
    schistosomiasis helminthic infection caused by Schistosoma spp.; transmitted from a snail intermediate host to human swimmers or bathers in freshwater        
    schizogony asexual reproduction in protozoans that is characterized by multiple cell divisions (one cell dividing to form many smaller cells)        
    scolex the head region of a cestode (tapeworm), which typically has suckers and/or hooks for attachment to the host        
    scrapie form of transmissible spongiform encephalopathy that primarily affects sheep        
    sebaceous gland a gland located in hair follicles that secretes sebum        
    sebum lipid-rich substance secreted by the sebaceous glands of the skin        
    secondary antibody antibody to which an enzyme is attached for use in ELISA assays; in direct and sandwich ELISAs, it is specific for the antigen being quantified, whereas in indirect ELISA, it is specific for the primary antibody        
    secondary immunodeficiency impaired immune response due to infection, metabolic disturbance, poor diet, stress, or other acquired factors        
    secondary infection second infection that develops after a primary infection as a result of the primary disease compromising immune defenses or antibiotics, thus eliminating protective microbiota        
    secondary lymphoid tissue one of two types of lymphatic tissue; comprises the spleen, lymph nodes, Peyer’s patches, and mucosa associated lymphoid tissue (MALT)        
    secondary response the adaptive immune response produced in response to a specific antigen to which the body has previously been exposed        
    secondary structure structure stabilized by hydrogen bonds between the carbonyl and amine groups of a polypeptide chain; may be an α-helix or a β-pleated sheet, or both        
    secretory vesicle membranous sac that carries molecules through the plasma membrane to be released (secreted) from the cell        
    selective IgA deficiency primary immunodeficiency in which individuals produce normal levels of IgG and IgM, but are unable to produce secretory IgA        
    selective media media that contain additives that encourage the growth of some bacteria while inhibiting others        
    selective toxicity desirable quality of an antimicrobial drug indicating that it preferentially kills or inhibits the growth of the target microbe while causing minimal or no harm to the host        
    semiconservative DNA replication pattern of DNA replication process whereby each of the two parental DNA strands acts as a template for new DNA to be synthesized, producing hybrid old- and new-strand daughter molecules        
    semicritical item object that contacts mucous membranes or nonintact skin but does not penetrate tissues; requires a high level of disinfection        
    seminal vesicles glands that contribute fluid to semen        
    semisynthetic antimicrobial chemically modified derivative of a natural antibiotic        
    sense strand strand of DNA that is not transcribed for gene expression; it is complementary to the antisense strand        
    sepsis systemic inflammatory response to an infection that results in high fever and edema, causing organ damage and possibly leading to shock and death        
    septate hyphae hyphae that contain walls between individual cells; characteristic of some fungi        
    septic arthritis see infectious arthritis        
    septic shock serious condition marked by the loss of blood pressure resulting from an inflammatory response against a systemic infection        
    septic the condition of being septicemic; having an infection in the blood        
    septicemia condition in which pathogens are multiplying in blood        
    septicemic plague form of plague that occurs when the bacterial pathogen gains access to the bloodstream        
    septum separating structure that forms during cell division; also describes the separating wall between cells in a filament        
    sequela (plural: sequelae) condition that arises as a consequence of a prior disease        
    serial dilution sequential transfer of known volumes of culture samples from one tube to another to perform a several-fold dilution of the original culture        
    seroconversion point in an infection at which antibody to a pathogen is detectible using an immunoassay        
    serotype strain or variation of the same species of bacteria; also called serovar        
    serovar specific strain of bacteria identified by agglutination using strain-specific antisera        
    serum fluid portion of the blood after clotting has occurred; generally lacks clotting factors        
    serum sickness systemic type III hypersensitivity reaction        
    sessile attached to a surface        
    severe combined immunodeficiency disease (SCID) genetic disorder resulting in impaired function of B cells and T cells        
    sex pilus specialized type of pilus that aids in DNA transfer between some prokaryotic cells        
    sheath part of the tail on a bacteriophage that contracts to introduce the viral DNA into the bacterium        
    shigellosis gastrointestinal illness caused by Shigella bacteria, also called bacillary dysentery        
    shingles acute and painful rash that forms following the reactivation of a latent chickenpox infection        
    shock extreme drop in blood pressure that, among other causes, can result from a strong immune response to the activity of toxins or response to bacterial products and can result in death        
    shuttle vector a plasmid that can move between bacterial and eukaryotic cells        
    side chain the variable functional group, R, attached to the α carbon of an amino acid        
    sign objective and measurable indication of a disease        
    silent mutation point mutation that results in the same amino acid being incorporated into the resulting polypeptide        
    simple microscope a type of microscope with only one lens to focus light from the specimen        
    simple staining a staining technique that uses a single dye        
    single-stranded binding protein protein that coats the single strands of DNA near each replication fork to prevent the single-stranded DNA from rewinding into a double helix        
    sinusitis inflammation of the sinuses        
    S-layer cell envelope layer composed of protein covering the cell walls of some bacteria and archaea; in some archaea, may function as the cell wall        
    slime layer a type of glycocalyx with unorganized layers of polysaccharides that aid bacterial adherence to surfaces        
    smear a thin layer of a specimen on a slide        
    smooth endoplasmic reticulum a type of endoplasmic reticulum that lacks ribosomes, is involved in the biosynthesis of lipids and in carbohydrate metabolism, and serves as the site of detoxification of toxic compounds within the cell        
    soft chancres soft, painful ulcers associated with the STI chancroid        
    soma cell body of a neuron        
    sonication method of microbial control that involves application of ultrasound waves to form cavitation within a solution, including inside cells, disrupting cell components as a result        
    Southern blot a technique in molecular genetics used to detect the presence of certain DNA sequences within a given DNA sample; DNA fragments within the sample are separated by agarose gel electrophoresis, immobilized on a membrane, and then exposed to a specific DNA probe labeled with a radioactive or fluorescent molecular beacon to aid in detection        
    specialized transduction transfer of a specific piece of bacterial chromosomal DNA near the site of integration by the phage        
    specificity the ability of the specific adaptive immune system to target specific pathogens or toxins        
    spike viral glycoprotein embedded within the viral capsid or envelope used for attachment to host cells        
    spirochetes a group of long, thin, spiral-shaped fastidious bacteria that includes the human pathogens that cause syphilis, Lyme disease, and leptospirosis        
    spleen abdominal organ consisting of secondary lymphoid tissue that filters blood and captures pathogens and antigens that pass into it; also contains specialized macrophages and dendritic cells that are crucial for antigen presentation        
    spliceosome protein complex containing small nuclear ribonucleoproteins that catalyzes the splicing out of intron-encoded RNA sequences from the primary transcript during RNA maturation in eukaryotes        
    spontaneous generation the now-disproven theory that life can arise from nonliving matter        
    spontaneous mutation, spontaneous mutations mutation not caused by a mutagen that occurs through DNA replication errors        
    sporadic disease an illness that occurs at relatively low levels with no discernible pattern or trend, frequently with no geographic focus        
    spores specialized cells that may be used for reproduction or may be specialized to withstand harsh conditions        
    sporotrichosis subcutaneous infection caused by the fungus Sporothrix schenkii, which causes skin lesions and can potentially spread to the lymphatic system; also known as rose gardener’s disease or rose thorn disease        
    sporulation the process by which a vegetative cell produces a dormant endospore        
    spread plate method a technique used for inoculating plates with diluted bacterial samples for the purpose of cell counting; the liquid sample is pipetted onto solid medium and spread uniformly across the plate        
    St. Louis encephalitis mosquito-borne viral infection of the brain that occurs primarily in the central and southern United States        
    stage the platform of a microscope on which slides are placed        
    staining the addition of stains or dyes to a microscopic specimen for the purpose of enhancing contrast        
    staphylococcal food poisoning gastrointestinal illness caused by toxins produced by Staphylococcus aureus        
    staphylolysins a class of staphylococcal exotoxins that are cytotoxic to skin cells and white blood cells        
    starch energy-storage polysaccharide in plants; composed of two types of glucose polymers: amylose and amylopectin        
    start codon AUG codon, specifying methionine, which is typically the codon that initiates translation        
    stationary phase interval during which the number of cells formed by cell division is equal to the number of cells dying        
    stereoisomers isomers that differ in the spatial arrangements of atoms        
    sterilant strong chemical that effectively kills all microbes and viruses in or on an inanimate item        
    sterile field specified area that is free of all vegetative microbes, endospores, and viruses        
    sterilization protocol that completely removes all vegetative cells, endospores, and viruses from an item        
    steroid lipid with complex, ringed structures found in cell membranes and hormones        
    sterol the most common type of steroid; contains an OH group at one specific position on one of the molecule’s carbon rings        
    sticky ends short, single-stranded complementary overhangs that may be produced when many restriction enzymes cut DNA        
    stigma light-sensing eyespot found in Euglena        
    stop codon (nonsense codon) one of three codons for which there is no tRNA with a complementary anticodon; a signal within the mRNA for termination of translation        
    stratum corneum a layer of dead, keratinized cells that forms the uppermost layer of the epidermis        
    strep throat (streptococcal pharyngitis) bacterial pharyngitis caused by Streptococcus pyogenes        
    streptococcal toxic shock-like syndrome (STSS) condition similar to staphylococcal toxic shock syndrome but with greater likelihood of bacteremia, necrotizing fasciitis, and acute respiratory distress syndrome        
    stroma a gel-like fluid that makes up much of a chloroplast’s volume, and in which the thylakoids floats        
    strongyloidiasis soil-transmitted intestinal infection caused by the helminth Strongyloides stercoralis        
    structural formula graphic representation of the molecular structure showing how the atoms are arranged        
    structural isomers molecules composed of the same numbers and types of atoms but with different bonding sequences        
    subacute bacterial endocarditis form of endocarditis in which damage to the valves of the heart occurs over months as a result of blood clot formation and immune-response-induced fibrosis of the valves        
    subclinical disease disease that does not present any signs or symptoms        
    subcutaneous mycosis any fungal infection that penetrates the epidermis and dermis to enter deeper tissues        
    substrate chemical reactants of an enzymatic reaction        
    substrate-level phosphorylation direct method of ATP production in which a high-energy phosphate group is removed from an organic molecule and added to an ADP molecule        
    subunit vaccine vaccine that contains only key antigens as opposed to whole pathogens        
    sugar-phosphate backbone alternating sugar-phosphate structure composing the framework of a nucleic acid strand that results from phosphodiester bond formation between nucleotides        
    sulfonamides (sulfa drugs) group of structurally related synthetic antimicrobial compounds that function as antimetabolites, competitively inhibiting an enzyme in the bacterial folic acid synthesis pathway        
    superantigen class of exotoxin that triggers a strong nonspecific immune response with excessive production of cytokines (cytokine storm) causing inflammation, high fever, shock, and, potentially, death        
    supercoiled extensive wrapping and twisting of a DNA molecule, allowing the DNA to fit within a small space        
    supercoiling process in which DNA is underwound or overwound to fit inside a cell        
    supercritical fluid molecule, commonly carbon dioxide, brought to high pressures to reach a state that has physical properties between those of liquids and gases, allowing it to effectively penetrate surfaces and cells to form carbonic acid, which lowers the pH of cells considerably, leading to sterilization        
    superinfection secondary infection that may develop as a result of long-term, broad-spectrum antimicrobial use        
    superoxide dismutase enzyme that catalyzes the breakdown of superoxide anions        
    suppurative producing pus; purulent        
    surfactant group of chemical compounds used for degerming; lower the surface tension of water, creating emulsions that mechanically carry away microorganisms        
    sweat gland one of numerous tubular glands embedded in the dermis that secretes the watery substance known as perspiration        
    symbiosis any interaction between different species that are associated with each other within a community        
    symptom subjective experience of disease felt by the patient        
    synapse junction between a neuron and another cell        
    syncytia multinucleated cells that form from the fusion of normal cells during infections or other processes        
    syndrome group of signs and symptoms characteristic of a particular disease        
    syngamy process in which haploid gametes fuse        
    synthetic antimicrobial antimicrobial developed from a chemical not found in nature        
    syphilis an STI caused by the bacterium Treponema pallidum        
    systemic autoimmune disease autoimmune disease that affect the organism as a whole, rather than a single organ        
    systemic infection infection that has spread to multiple locations or body systems        
    systemic inflammatory response syndrome (SIRS) severe inflammatory response to the presence of microbes in the blood; can lead to sepsis        
    systemic lupus erythematosus (SLE) systemic autoimmune disease producing inflammatory type III hypersensitivities as antibodies form immune complexes with nuclear and cytoplasmic antigens        
    systemic mycosis a fungal infection that spreads throughout the body        
    T-cell receptors (TCR) molecules on T cells involved in the recognition of processed foreign epitopes presented with MHC I or MHC II        
    T lymphocyte lymphocyte that serves as the central orchestrator, bridging humoral, cellular, and innate immunity, and serves as the effector cells of cellular immunity; T cell        
    taeniasis infection caused by Taenia or Diphyllobothrium        
    tail fiber long protein component on the lower part of a phage used for specific attachment to bacterial cell        
    tail pins points extended at the base of a bacteriophage sheath that, along with tail fibers, lead to phage attachment to a bacterial cell        
    tapeworms segmented, hermaphroditic, parasitic flatworms (Platyhelminthes)        
    tartar calcified heavy plaque on teeth, also called dental calculus taxonomy the classification, description, identification, and naming of living organisms        
    T-dependent antigen a protein antigen that is only capable of activating a B cell with the cooperation of a helper T cell        
    TDP thermal death point is the lowest temperature at which all microorganisms are killed in a 10-minute exposure        
    TDT thermal death time is the length of time needed to kill all microorganisms in a sample at a given temperature        
    telomerase enzyme that attaches to the end of a linear chromosome and adds nucleotides to the 3’ end of one of the DNA strands, maintaining the telomere sequence, thus preventing loss of DNA from the end of the chromosome        
    telomere repetitive, noncoding sequence found at the end of a linear eukaryotic chromosome that protects the genes near the end of the chromosome from deletion as the DNA molecule is repeatedly replicated        
    temperate phage bacteriophage that can incorporate viral genome into the host cell chromosome and replicate with the host cell until new viruses are produced; a phage that undergoes the lysogenic cycle        
    teratogenic able to disrupt the normal development of a fetus in utero        
    terbinafine antifungal drug of the allylamine class that is used topically for the treatment of dermatophytic skin infections        
    termination of DNA replication stage of replication during which DNA replication is halted once the chromosome has been fully replicated        
    termination of transcription stage of transcription that occurs when RNA polymerase has reached specific DNA sequences, leading to release of the enzyme from the DNA template, freeing the RNA transcript and, thus, halting transcription        
    termination of translation stage of translation during which a nonsense codon aligns with the A site, signaling release factors to release of the polypeptide, leading to the dissociation of the small and large ribosomal subunits from the mRNA and from each other        
    tertiary structure large-scale, three-dimensional structure of a polypeptide        
    test sensitivity probability that a diagnostic test will find evidence of the targeted disease when the pathogen is present        
    test specificity probability that a diagnostic test will not find evidence of the targeted disease when the pathogen is absent        
    testes (singular testis) pair of glands located in the scrotum of males that produce sperm and testosterone        
    tetanus bacterial disease caused by exotoxin produced by Clostridium tetani that causes a rigid paralysis        
    tetracyclines class of protein synthesis inhibitors that bind to the 30S subunit, blocking the association of tRNAs with the ribosome during translation        
    TH1 cells subtype of T cells that stimulate cytotoxic T cells, macrophages, neutrophils, and NK cells        
    TH17 cells subtype of T cell that are essential for defense against specific pathogens and infections, such as chronic mucocutaneous infections with C. albicans        
    TH2 cells subtype of T cells that stimulate B cells and direct their differentiation; also involved in directing antibody class switching        
    thallus body of fleshy fungi (more generally, a body without a root, stem, or leaf) that commonly co-occurs with HIV infection; the microbes move to the lymphatic system in the groin        
    thermophile a microorganism that grows best at warm temperatures, typically between about 50 °C and 80 °C        
    thin sections thin slices of tissue for examination under a TEM        
    thioglycolate medium medium designed to test the aerotolerance of bacteria; it contains a low concentration of agar to allow motile bacteria to move throughout the medium        
    thioglycolate tube culture contains reducing medium through which oxygen diffuses from the tube opening, producing a range of oxygen environments down the length of the tube        
    thrombocytes see platelets        
    thylakoids a highly dynamic collection of membranous sacs found in the stroma of chloroplasts; site of photosynthesis        
    thymic selection a three-step process of negative and positive selection of T cells in the thymus        
    thymine dimer covalent linkage between two adjacent thymine bases on exposure to ultraviolet radiation        
    thymine pyrimidine nitrogenous base found only in DNA nucleotides        
    tincture solution of an antiseptic compound dissolved in alcohol        
    T-independent antigen a nonprotein antigen that can activate a B cell without cooperation from a helper T cell        
    tinea any cutaneous fungal infection caused by dermatophytes, such as tinea corporis, tinea capitis, tinea cruris, and tinea pedis        
    tinea capitis cutaneous mycosis of the scalp; also known as ringworm of the scalp        
    tinea corporis cutaneous mycosis of the body; also known as ringworm of the body        
    tinea cruris cutaneous mycosis of the groin region; also known as jock itch        
    tinea pedis cutaneous mycosis of the feet; also known as athlete’s foot        
    tissue tropism tendency of most viruses to infect only certain tissue types within a host        
    titer concentration obtained by titration; the reciprocal of a measurement of biological activity determined by finding the dilution of an unknown (e.g., antigen-specific antibody in an antiserum) that shows the defined end-point; always expressed as a whole number        
    tolerance lack of an anti-self immune response        
    toll-like receptors (TLRs) pathogen recognition receptors (PRRs) that may be found on the external surface of phagocytes or facing inward in interior compartments        
    tonsillitis inflammation of the tonsils        
    topoisomerase type of enzyme that helps maintain the structure of supercoiled chromosomes, preventing overwinding of DNA during certain cellular processes like DNA replication        
    topoisomerase II enzyme responsible for facilitating topological transitions of DNA, relaxing it from its supercoiled state        
    total magnification in a light microscope is a value calculated by multiplying the magnification of the ocular by the magnification of the objective lenses        
    toxemia presence of toxins in the blood        
    toxic shock syndrome severe condition marked by the loss of blood pressure and blood clot formation caused by a bacterial superantigen, toxic shock syndrome toxin        
    toxigenicity ability of a pathogen to produce toxins to cause damage to host cells        
    toxin poison produced by a pathogen        
    toxoid vaccine vaccine that contains inactivated bacterial toxins        
    toxoplasmosis typically asymptomatic protozoan infection caused by Toxoplasma spp. and transmitted through contact with cysts in cat feces; infections in pregnant women may cause birth defects or miscarriage        
    trace element indispensable element present in cells in lower amounts than macronutrients; also called micronutrient        
    trachea also known as the windpipe, this is a stiffened tube of cartilage that runs from the larynx to the bronchi        
    trachoma a type of conjunctivitis, caused by Chlamydia trachomatis, that is a major cause of preventable blindness        
    transcription bubble region of unwinding of the DNA double helix during transcription        
    transcription factors proteins encoded by regulatory genes that function by influencing the binding of RNA polymerase to the promoter and allowing its progression to transcribe structural genes        
    transcription process of synthesizing RNA using the information encoded in DNA        
    transcriptomics the study of the entire collection of mRNA molecules produced by cells; involves monitoring differences in gene expression patterns between cells at the mRNA level        
    transduction mechanism of horizontal gene transfer in bacteria in which genes are transferred through viral infection        
    transendothelial migration process by which circulating leukocytes exit the bloodstream via the microvascular endothelium        
    transfection the introduction of recombinant DNA molecules into eukaryotic hosts        
    transformation mechanism of horizontal gene transfer in bacteria in which naked environmental DNA is taken up by a bacterial cell        
    transgenic describing an organism into which foreign DNA from a different species has been introduced        
    transient microbiota microorganisms, sometimes pathogenic, that are only temporarily found in the human body        
    transition reaction reaction linking glycolysis to the Krebs cycle, during which each pyruvate is decarboxylated and oxidized (forming NADH), and the resulting two-carbon acetyl group is attached to a large carrier molecule called coenzyme A, resulting in the formation of acetyl-CoA and CO; also called the bridge reaction        
    translation (protein synthesis) process of protein synthesis whereby a ribosome decodes an mRNA message into a polypeptide product        
    transmissible spongiform encephalopathy degenerative disease caused by prions; leads to the death of neurons in the brain        
    transmission electron microscope (TEM) a type of electron microscope that uses an electron beam, focused with magnets, that passes through a thin specimen        
    transmittance the amount of light that passes through a medium        
    transparency the property of allowing light to pass through        
    transport vesicle membranous sac that carries molecules between various components of the endomembrane system        
    transposition process whereby a DNA sequence known as a transposon independently excises from one location in a DNA molecule and integrates elsewhere        
    transposon (transposable element) molecule of DNA that can independently excise from one location in a DNA molecule and integrate into the DNA elsewhere        
    trench fever louseborne disease caused by Bartonella quintana and characterized by high fever, body aches, conjunctivitis, ocular pain, severe headaches, and severe bone pain        
    trench mouth a severe form of gingivitis, also called acute necrotizing ulcerative gingivitis        
    treponemal serologic tests tests for syphilis that measure the amount of antibody directed against antigens associated with Treponema pallidum        
    triacylglycerol three fatty acids chemically linked to a glycerol molecule; also called a triglyceride        
    triazoles ergosterol biosynthesis inhibitors used to treat several types of systemic yeast infections; exhibit more selective toxicity than the imidazoles and are associated with fewer side effects        
    tricarboxylic acid cycle see Krebs cycle        
    trichinosis soil-transmitted intestinal infection caused by the nematode Trichinella spiralis; associated with cyst formation        
    trichomoniasis a common STI caused by Trichomonas vaginalis        
    trichuriasis intestinal infection caused by the whipworm Trichuris trichiura        
    triglyceride three fatty acids chemically linked to a glycerol molecule; also called a triacylglycerol        
    trimethoprim synthetic antimicrobial compound that functions as an antimetabolite to an enzyme in the bacterial folic acid synthesis pathway        
    tRNA small type of stable RNA that carries the correct amino acid to the site of protein synthesis in the ribosome and base pairs with the mRNA to allow the amino acid it carries to be inserted in the polypeptide chain being synthesized        
    trophozoite a life cycle phase in which protists are actively feeding and growing        
    tubercle small, rounded lesion        
    tuberculosis life-threatening form of microbial infection marked by the presence of acid-fast bacteria growing in nodules (especially in the lungs)        
    tularemia infection of the lymphatic system by Francisella tularensis; also known as rabbit fever        
    tumbles (tumbling) random, circuitous movement of a bacterial cell, propelled by clockwise flagellar rotation        
    tumor collection or aggregate of cells; can be benign (noncancerous) or malignant (cancerous)        
    tumor-inducing (Ti) plasmid a naturally occurring plasmid of the bacterium Agrobacterium tumefaciens that researchers use as a shuttle vector to introduce a desired DNA fragment into plant cells        
    turbidity cloudiness of a culture due to refraction of light by cells and particles        
    two-photon microscope a microscope that uses long-wavelength or infrared light to fluoresce fluorochromes in the specimen        
    tympanic membrane also referred to as the ear drum, this structure separates the outer and middle ear        
    type 1 diabetes mellitus hyperglycemia caused by an autoimmune disease affecting insulin production by β cells of the pancreas        
    type I hypersensitivity rapid-onset allergic reaction due to cross-linking of antigen-specific IgE on the outside of mast cells, resulting in release of inflammatory mediators        
    type II hypersensitivity cytotoxic reaction triggered by IgG and IgM antibodies binding to antigens on cell surfaces        
    type III hypersensitivity inflammatory reaction induced by formation of immune complexes and their deposition in tissues and blood vessels        
    type IV hypersensitivity delayed T-cell-mediated inflammatory reaction that takes longer to manifest than the first three hypersensitivity types, due to the need for activation of antigen-presenting cell and T-cell subsets        
    typhoid fever serious illness caused by infection with certain serotypes of Salmonella        
    UHT pasteurization method of pasteurization that exposes milk to ultra-high temperatures (near 140 °C) for a few seconds, effectively sterilizing it so that it can be sealed and stored for long periods without refrigeration        
    ulcer open sore        
    ultramicrotome a device that cuts thin sections for electron microscopy        
    unit membrane biological membrane composed of two layers of phospholipid molecules with the nonpolar tails associating to form a hydrophobic barrier between the polar heads; also called lipid bilayer        
    unsaturated fatty acid lipid with hydrocarbon chains containing one or more carbon-carbon double bonds and subsequently fewer than the maximum number of hydrogen atoms per chain        
    uracil pyrimidine nitrogenous base found only in RNA nucleotides        
    ureter duct that transports urine from the kidneys to the urinary bladder        
    ureteritis inflammation of the ureter        
    urethra duct through which urine passes from the urinary bladder to leave the body through the urinary meatus        
    urethritis inflammation of the urethra        
    urinary bladder an organ that stores urine until it is ready to be excreted        
    urinary meatus the opening through which urine leaves the body        
    use-dilution test a technique for determining the effectiveness of a chemical disinfectant on a surface; involves dipping a surface in a culture of the targeted microorganism, disinfecting the surface, and then transferring the surface to a fresh medium to see if bacteria will grow        
    uterus female reproductive organ in which a fertilized egg implants and develops        
    vaccination inoculation of a patient with attenuated pathogens or antigens to activate adaptive immunity and protect against infection        
    vagina female reproductive organ that extends from the vulva to the cervix        
    vaginitis inflammation of the vagina        
    vaginosis an infection of the vagina caused by overgrowth of resident bacteria        
    vancomycin cell wall synthesis inhibitor of the glycopeptide class        
    vancomycin-intermediate Staphylococcus aureus (VISA) pathogen with intermediate vancomycin resistance due to increased targets for and trapping of vancomycin in the outer cell wall        
    vancomycin-resistant enterococci (VRE) pathogens resistant to vancomycin through a target modification of peptidoglycan subunit peptides that inhibit binding by vancomycin        
    vancomycin-resistant Staphylococcus aureus (VRSA) pathogen with resistance to vancomycin that has arisen as a result of the horizontal gene transfer of vancomycin resistance genes from VRE        
    variolation the historical practice of inoculating a healthy patient with infectious material from a person infected with smallpox in order to promote immunity to the disease        
    vas deferens pair of ducts in the male reproductive system that conduct sperm from the testes and seminal fluid to the ejaculatory duct        
    vasculitis inflammation affecting blood vessels (either arteries or veins)        
    VDRL (Venereal Disease Research Laboratory) test test for syphilis that detects anti-treponemal antibodies to the phospholipids produced due to the tissue destruction by Treponema pallidum; antibodies are detected through a flocculation reaction with cardiolipin extracted from beef heart tissue        
    vector animal (typically an arthropod) that transmits a pathogen from one host to another host; DNA molecules that carry DNA fragments from one organism to another        
    vegetative cell a cell that is actively growing and dividing, and does not contain an endospore        
    vehicle transmission transfer of a pathogen between hosts via contaminated food, water, or air        
    vein blood vessel that returns blood from the tissues to the heart for recirculation        
    vertical direct transmission transfer of a pathogen from mother to child during pregnancy, birth, or breastfeeding        
    vertical gene transfer transfer of genes from parent to offspring        
    viable cell live cell; live cells are usually detected as colony-forming units        
    viable plate count direct method of measuring microbial growth in a culture; the number of viable or live cells is usually expressed in CFU/mL        
    viral conjunctivitis inflammation of the conjunctiva caused by a viral infection        
    viral envelope lipid membrane obtained from phospholipid membranes of the cell that surrounds the capsid        
    viral hemagglutination inhibition assay assay used to quantify the amount of neutralizing antibody against a virus by showing a decrease in hemagglutination caused by a standardized amount of virus        
    viral titer number of virions per unit volume        
    viremia presence of virus in blood        
    viricide chemical or physical treatment that destroys or inactivates viruses        
    virion inert particle that is the reproductive form of a virus        
    viroid infectious plant pathogen composed of RNA        
    virology the study of viruses        
    virulence degree to which an organism is pathogenic; severity of disease signs and symptoms        
    virulence factor product of a pathogen that assists in its ability to cause infection and disease        
    virulent phage bacteriophage for which infection leads to the death of the host cell; a phage that undergoes the lytic cycle        
    virus an acellular microorganism, consisting of proteins and genetic material (DNA or RNA), that can replicate itself by infecting a host cell        
    virusoid small piece of RNA associated with larger RNA of some infectious plant viruses        
    volutin inclusions of polymerized inorganic phosphate; also called metachromatic granules        
    vulva the female external genitalia        
    water activity water content of foods or other materials        
    wavelength the distance between one peak of a wave and the next peak        
    Weil’s disease advanced stage of leptospirosis in which the kidney and liver become seriously infected        
    West African trypanosomiasis chronic form of African trypanosomiasis caused by Trypanosoma brucei gambiense        
    West Nile encephalitis mosquito-borne disease caused by the West Nile virus (WNV) that can result in swelling of the brain and death in severe cases        
    western blot technique used to detect the presence of a certain protein within a given protein sample in which proteins within the sample are separated by PAGE, immobilized on a membrane, and then exposed first to an antibody that binds to the protein of interest and then second to an antibody equipped with a molecular beacon that will bind to the first antibody        
    western equine encephalitis serious but rare mosquito-borne viral infection of the brain that is found primarily in the central and western United States        
    wet mount a slide preparation technique in which a specimen is placed on the slide in a drop of liquid        
    wheal-flare reaction localized type I hypersensitivity reaction, involving a raised, itchy bump (wheal) and redness (flare), to injected allergen        
    whooping cough common name for pertussis        
    wild type phenotype of an organism that is most commonly observed in nature        
    Winterbottom’s sign acute swelling of lymph nodes at the back of the neck that is an early sign of African trypanosomiasis        
    wobble position third position of a codon that, when changed, typically results in the incorporation of the same amino acid because of the degeneracy of the genetic code        
    World Health Organization (WHO) international public health organization within the United Nations; monitors and communicates international public health information and coordinates international public health programs and emergency interventions        
    xenobiotic compound synthesized by humans and introduced to an environment in much higher concentrations than expected in nature        
    xenograft transplanted tissue from a donor that is of a different species than the recipient        
    X-linked agammaglobulinemia genetic disorder resulting in an inability to produce antibodies        
    x-y mechanical stage knobs knobs on a microscope that are used to adjust the position of the specimen on the stage surface, generally to center it directly above the light        
    yeast any unicellular fungus        
    yeast infection fungal infection of the vagina typically caused by an overgrowth of resident Candida spp.        
    yellow fever mild to potentially fatal mosquito-borne viral disease caused by the yellow fever virus        
    Ziehl-Neelsen technique a method of acid-fast staining that uses heat to infuse the primary stain, carbolfuchsin, into acid-fast cells        
    zone of inhibition clear zone around a filter disk impregnated with an antimicrobial drug, indicating growth inhibition due to the antimicrobial drug        
    zoonosis see zoonotic disease        
    zoonotic disease any disease that is transmitted to humans by animals        
    zooplankton heterotrophic plankton        
    Z-scheme electron flow seen in noncyclic photophosphorylation in plants, algae, and cyanobacteria due to the use of both PSI and PSII        
    zygospores spores used by Zygomycetes for sexual reproduction; they have hard walls formed from the fusion of reproductive cells from two individuals