Question 1

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

Accepted Answer

Viruses lack cellular structure and metabolic enzymes, while bacteria are cellular and metabolically active.

Question 2

A scientist is culturing bacteriophages using the plaque method. What is the principle behind this technique?

Accepted Answer

Plaques are clear zones on a bacterial lawn caused by lysis of bacteria by phages.

Question 3

Which of the following best describes the difference between the lytic and lysogenic cycles of bacteriophages?

Accepted Answer

The lytic cycle results in immediate destruction of the host cell, while the lysogenic cycle involves integration of viral DNA into the host genome without immediate lysis.

Question 4

A patient is diagnosed with shingles. Which type of viral infection does this represent?

Accepted Answer

Latent infection

Question 5

Which of the following is a key difference between exotoxins and endotoxins?

Accepted Answer

Exotoxins are secreted by living bacteria, while endotoxins are released upon bacterial cell death.

Question 6

The LD50 of botulinum toxin is $$0.03\ \mathrm{ng/kg}$$, and the LD50 of Salmonella toxin is $$12\ \mathrm{mg/kg}. $$Which toxin is more potent?

Accepted Answer

Botulinum toxin, because it requires a much lower dose to kill 50% of test animals.

Question 7

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

Accepted Answer

Siderophores sequester iron from the host, making it available for bacterial growth.

Question 8

Which of the following is an example of antigenic variation, and why does it make influenza vaccines less effective over time?

Accepted Answer

Influenza virus changes its surface antigens, allowing it to evade immune detection and requiring new vaccines each season.

Question 9

Which of the following is a principal event in the multiplication cycle of an enveloped DNA-containing animal virus?

Accepted Answer

Attachment, entry, uncoating, biosynthesis, maturation, and release by budding.

Question 10

Which of the following best defines herd immunity?

Accepted Answer

A form of immunity that occurs when a high percentage of the population is immune, reducing the spread of disease.

Question 11

A hospital infection control officer investigates an outbreak where 40 employees developed nausea and vomiting after eating green beans in the cafeteria. What type of epidemiologic investigation is this?

Accepted Answer

Analytical epidemiology

Question 12

Which of the following is a function shared by capsules and M proteins in bacterial pathogenicity?

Accepted Answer

Both inhibit phagocytosis by host immune cells.

Question 13

Which of the following is a mechanism by which bacteria avoid destruction by phagocytes?

Accepted Answer

Formation of capsules to prevent phagocyte adherence

Question 14

Which of the following best describes the classical pathway of complement activation?

Accepted Answer

It is triggered by antigen-antibody complexes binding to C1.

Question 15

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

Accepted Answer

Interferons induce antiviral states in neighboring cells, inhibiting viral replication.

Question 16

Which class of antibody is most likely to protect you from a common cold?

Accepted Answer

IgA

Question 17

Which of the following best describes the outcome of clonal selection in adaptive immunity?

Accepted Answer

Production of plasma cells and memory cells specific to an antigen.

Question 18

Which antibodies may activate the complement system, and which are usually associated with agglutination?

Accepted Answer

IgM and IgG activate complement; IgM is usually associated with agglutination.

Question 19

A patient receives an injection of gamma globulin for immediate protection against hepatitis. What type of adaptive immunity is this?

Accepted Answer

Artificially acquired passive immunity

Question 20

Which of the following best describes the role of natural killer (NK) cells in antibody-dependent cell-mediated cytotoxicity (ADCC)?

Accepted Answer

NK cells recognize and kill target cells coated with antibodies, even though NK cells are not immunologically specific.

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