Question 1

Which of the following best distinguishes a virus from a bacterium?

Accepted Answer

Viruses lack both ribosomes and metabolic enzymes, while bacteria possess both.

Question 2

A researcher is culturing animal viruses and needs a cell line that can be maintained indefinitely for repeated experiments. Which type of cell line should they use, and why?

Accepted Answer

Continuous cell lines, because they can divide indefinitely and are more practical for long-term studies.

Question 3

Which of the following best describes the difference between a latent and a persistent viral infection?

Accepted Answer

Latent infections remain dormant and can reactivate, while persistent infections involve continuous viral production.

Question 4

A patient develops fever and chills after a cardiac catheterization, but the water and catheters used were sterile. Which test should have been performed to detect the likely cause of these symptoms?

Accepted Answer

The Limulus Amebocyte Lysate (LAL) assay to detect endotoxins.

Question 5

Which of the following statements about Koch’s postulates is correct?

Accepted Answer

Some pathogens cannot be cultured in artificial media, making exceptions to Koch’s postulates necessary.

Question 6

A patient is exposed to botulinum toxin ($$LD_{50} = 0.03\ \mathrm{ng/kg}) $$and Salmonella toxin ($$LD_{50} = 12\ \mathrm{mg/kg}). $$Which toxin is more potent, and why?

Accepted Answer

Botulinum toxin, because a much lower dose is required to kill 50% of the test population.

Question 7

Which of the following best explains why the influenza vaccine does not provide long-term protection?

Accepted Answer

Influenza viruses undergo antigenic variation, frequently changing their surface proteins.

Question 8

Which of the following is an example of microbial antagonism?

Accepted Answer

Normal microbiota outcompete pathogens for nutrients, preventing their colonization.

Question 9

A patient receives an injection of gamma globulin after exposure to hepatitis A. Which type of adaptive immunity is this?

Accepted Answer

Artificially acquired passive immunity.

Question 10

Which of the following best describes the function of siderophores in bacterial pathogenicity?

Accepted Answer

They bind iron tightly, allowing bacteria to compete with host iron-binding proteins.

Question 11

Which of the following is a correct sequence in the pattern of disease progression?

Accepted Answer

Incubation period → prodromal period → period of illness → period of decline → period of convalescence

Question 12

Which of the following best describes the mechanism of action of A-B toxins?

Accepted Answer

The B component binds to the host cell, allowing the A component to enter and disrupt cellular function.

Question 13

Which of the following is a function of interferons in innate immunity?

Accepted Answer

They induce uninfected cells to produce antiviral proteins that inhibit viral replication.

Question 14

A patient is diagnosed with listeriosis, which has a morbidity of 121 and a mortality of 13 in a given year. West Nile encephalitis has a morbidity of 5,674 and a mortality of 286. Which disease is more likely to be fatal, and how is this determined?

Accepted Answer

Listeriosis, because the mortality-to-morbidity ratio is higher.

Question 15

Which of the following best describes the role of Toll-like receptors (TLRs) in innate immunity?

Accepted Answer

They recognize pathogen-associated molecular patterns (PAMPs) and activate immune responses.

Question 16

Which antibody class is most likely to protect you from a common cold, and why?

Accepted Answer

IgA, because it is abundant in mucosal secretions such as saliva and mucus.

Question 17

A patient is infected with a bacterium that produces both coagulase and kinase. What is the likely effect of these enzymes on the infection process?

Accepted Answer

Coagulase forms clots to protect bacteria, while kinase dissolves clots to allow spread, so simultaneous production would be counterproductive.

Question 18

Which of the following is a correct statement about the complement system?

Accepted Answer

It can be activated by three pathways: classical, alternative, and lectin.

Question 19

Which of the following best describes the function of natural killer (NK) cells?

Accepted Answer

They destroy cells that lack MHC class I molecules by releasing perforin and granzymes.

Microbiology Study Guide: Step-by-Step Guidance for Key Concepts

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