15.E: Microbial Mechanisms of Pathogenicity (Exercises)
15.1: Characteristics of Infectious Diseases
In an infection, a microorganism enters a host and begins to multiply. Some infections cause disease, which is any deviation from the normal function or structure of the host. Signs of a disease are objective and are measured. Symptoms of a disease are subjective and are reported by the patient. Diseases can either be noninfectious (due to genetics and environment) or infectious (due to pathogens).
Multiple Choice
Which of the following would be a sign of an infection?
- muscle aches
- headache
- fever
- nausea
- Answer
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C
Which of the following is an example of a noncommunicable infectious disease?
- infection with a respiratory virus
- food poisoning due to a preformed bacterial toxin in food
- skin infection acquired from a dog bite
- infection acquired from the stick of a contaminated needle
- Answer
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B
During an oral surgery, the surgeon nicked the patient’s gum with a sharp instrument. This allowed Streptococcus , a bacterium normally present in the mouth, to gain access to the blood. As a result, the patient developed bacterial endocarditis (an infection of the heart). Which type of disease is this?
- iatrogenic
- nosocomial
- vectors
- zoonotic
- Answer
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A
Which period is the stage of disease during which the patient begins to present general signs and symptoms?
- convalescence
- incubation
- illness
- prodromal
- Answer
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D
A communicable disease that can be easily transmitted from person to person is which type of disease?
- contagious
- iatrogenic
- acute
- nosocomial
- Answer
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A
Fill in the Blank
A difference between an acute disease and chronic disease is that chronic diseases have an extended period of __________.
- Answer
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illness
A person steps on a rusty nail and develops tetanus. In this case, the person has acquired a(n) __________ disease.
- Answer
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noncommunicable
Short Answer
Brian goes to the hospital after not feeling well for a week. He has a fever of 38 °C (100.4 °F) and complains of nausea and a constant migraine. Distinguish between the signs and symptoms of disease in Brian’s case.
Critical Thinking
Two periods of acute disease are the periods of illness and period of decline. (a) In what way are both of these periods similar? (b) In terms of quantity of pathogen, in what way are these periods different? (c) What initiates the period of decline?
In July 2015, a report 1 was released indicating the gram-negative bacterium Pseudomonas aeruginosa was found on hospital sinks 10 years after the initial outbreak in a neonatal intensive care unit. P. aeruginosa usually causes localized ear and eye infections but can cause pneumonia or septicemia in vulnerable individuals like newborn babies. Explain how the current discovery of the presence of this reported P. aeruginosa could lead to a recurrence of nosocomial disease.
15.2: How Pathogens Cause Disease
Koch’s postulates are used to determine whether a particular microorganism is a pathogen. Molecular Koch’s postulates are used to determine what genes contribute to a pathogen’s ability to cause disease. Virulence, the degree to which a pathogen can cause disease, can be quantified by calculating either the ID50 or LD50 of a pathogen on a given population. Primary pathogens are capable of causing pathological changes associated with disease in a healthy individual.
Multiple Choice
Which of the following is a pathogen that could not be identified by the original Koch’s postulates?
- Staphylococcus aureus
- Pseudomonas aeruginosa
- Human immunodeficiency virus
- Salmonella enterica serovar Typhimurium
- Answer
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C
Pathogen A has an ID 50 of 50 particles, pathogen B has an ID 50 of 1,000 particles, and pathogen C has an ID 50 of 1 × 10 6 particles. Which pathogen is most virulent?
- pathogen A
- pathogen B
- pathogen C
- Answer
-
A
Which of the following choices lists the steps of pathogenesis in the correct order?
- invasion, infection, adhesion, exposure
- adhesion, exposure, infection, invasion
- exposure, adhesion, invasion, infection
- disease, infection, exposure, invasion
- Answer
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C
Fill in the Blank
A(n) __________ pathogen causes disease only when conditions are favorable for the microorganism because of transfer to an inappropriate body site or weakened immunity in an individual.
- Answer
-
opportunistic
The concentration of pathogen needed to kill 50% of an infected group of test animals is the __________.
- Answer
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LD 50
A(n) __________ infection is a small region of infection from which a pathogen may move to another part of the body to establish a second infection.
- Answer
-
focal
Cilia, fimbriae, and pili are all examples of structures used by microbes for __________.
- Answer
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adhesion
Critical Thinking
Diseases that involve biofilm-producing bacteria are of serious concern. They are not as easily treated compared with those involving free-floating (or planktonic) bacteria. Explain three reasons why biofilm formers are more pathogenic.
A microbiologist has identified a new gram-negative pathogen that causes liver disease in rats. She suspects that the bacterium’s fimbriae are a virulence factor. Describe how molecular Koch’s postulates could be used to test this hypothesis.
Acupuncture is a form of alternative medicine that is used for pain relief. Explain how acupuncture could facilitate exposure to pathogens.
15.3: Virulence Factors
Virulence factors contribute to a pathogen’s ability to cause disease. Exoenzymes and toxins allow pathogens to invade host tissue and cause tissue damage. Exoenzymes are classified according to the macromolecule they target and exotoxins are classified based on their mechanism of action. Bacterial toxins include endotoxin and exotoxins. Endotoxin is the lipid A component of the LPS of the gram-negative cell envelope. Exotoxins are proteins secreted mainly by gram-positive bacteria.
Multiple Choice
Which of the following would be a virulence factor of a pathogen?
- a surface protein allowing the pathogen to bind to host cells
- a secondary host the pathogen can infect
- a surface protein the host immune system recognizes
- the ability to form a provirus
- Answer
-
A
You have recently identified a new toxin. It is produced by a gram-negative bacterium. It is composed mostly of protein, has high toxicity, and is not heat stable. You also discover that it targets liver cells. Based on these characteristics, how would you classify this toxin?
- superantigen
- endotoxin
- exotoxin
- leukocidin
- Answer
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C
Which of the following applies to hyaluronidase?
- It acts as a spreading factor.
- It promotes blood clotting.
- It is an example of an adhesin.
- It is produced by immune cells to target pathogens.
- Answer
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A
Phospholipases are enzymes that do which of the following?
- degrade antibodies
- promote pathogen spread through connective tissue.
- degrade nucleic acid to promote spread of pathogen
- degrade cell membranes to allow pathogens to escape phagosomes
- Answer
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D
Fill in the Blank
The glycoprotein adhesion gp120 on HIV must interact with __________ on some immune cells as the first step in the process of infecting the cell.
- Answer
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CD4
Adhesins are usually located on __________ of the pathogen and are composed mainly of __________ and __________.
- Answer
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surface; proteins; sugars
The Shiga and diphtheria toxins target __________ in host cells.
- Answer
-
protein synthesis
Antigenic __________ is the result of reassortment of genes responsible for the production of influenza virus spike proteins between different virus particles while in the same host, whereas antigenic __________ is the result of point mutations in the spike proteins.
- Answer
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shift; drift
Critical Thinking
Two types of toxins are hemolysins and leukocidins. (a) How are these toxins similar? (b) How do they differ?
Imagine that a mutation in the gene encoding the cholera toxin was made. This mutation affects the A-subunit, preventing it from interacting with any host protein. (a) Would the toxin be able to enter into the intestinal epithelial cell? (b) Would the toxin be able to cause diarrhea?
15.4: Aseptic Techniques
Fungal and parasitic pathogens use pathogenic mechanisms and virulence factors that are similar to those of bacterial pathogens. Fungi initiate infections through the interaction of adhesins with receptors on host cells. Some fungi produce toxins and exoenzymes involved in disease production and capsules that provide protection of phagocytosis. Protozoa adhere to target cells through complex mechanisms and can cause cellular damage through release of cytopathic substances.
Multiple Choice
Which of the following is a major virulence factor for the fungal pathogen Cryptococcus?
- hemolysin
- capsule
- collagenase
- fimbriae
- Answer
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B
Which of the following pathogens undergoes antigenic variation to avoid immune defenses?
- Candida
- Cryptococcus
- Plasmodium
- Giardia
- Answer
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C
Fill in the Blank
Candida can invade tissue by producing the exoenzymes __________ and __________.
- Answer
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protease and phospholipase
The larval form of Schistosoma mansoni uses a __________ to help it gain entry through intact skin.
- Answer
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protease
Short Answer
Describe the virulence factors associated with the fungal pathogen Aspergillus.
Explain how helminths evade the immune system.
Footnotes
- 1 C. Owens. “ P. aeruginosa survives in sinks 10 years after hospital outbreak.” 2015. http://www.healio.com/infectious-disease/nosocomial-infections/news/online/%7B5afba909-56d9-48cc-a9b0-ffe4568161e8%7D/p-aeruginosa-survives-in-sinks-10-years-after-hospital-outbreak