Glossary

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Words (or words that have the same definition)	The definition is case sensitive	(Optional) Image to display with the definition [Not displayed in Glossary, only in pop-up on pages]	(Optional) Caption for Image	(Optional) External or Internal Link	(Optional) Source for Definition
(Eg. "Genetic, Hereditary, DNA ...")	(Eg. "Relating to genes or heredity")		The infamous double helix	bio.libretexts.org/	CC-BY-SA; Delmar Larsen

Glossary Entries
Word(s)	Definition	Image	Caption	Link	Source
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 P_i
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 Cytophaga, Fusobacterium, 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 aureus, S. 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 (P_i)	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 P_i 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
T_H1 cells	subtype of T cells that stimulate cytotoxic T cells, macrophages, neutrophils, and NK cells
T_H17 cells	subtype of T cell that are essential for defense against specific pathogens and infections, such as chronic mucocutaneous infections with C. albicans
T_H2 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 (T_i) 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

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