Question 1

Which of the following best describes the difference between pathogenicity and virulence?

Accepted Answer

Pathogenicity is the ability to cause disease, while virulence is the degree of pathogenicity.

Question 2

A patient is diagnosed with gas gangrene after a traumatic injury. Which portal of entry and pathogen are most likely responsible?

Accepted Answer

Skin or parenteral route; Clostridium perfringens

Question 3

Which of the following best explains why Streptococcus pneumoniae with a capsule is more virulent than without a capsule?

Accepted Answer

The capsule impairs phagocytosis by host immune cells.

Question 4

Which of the following toxins has the lowest LD50 and is therefore the most potent?

Accepted Answer

Botulinum toxin

Question 5

A patient presents with fever, shock, and disseminated intravascular coagulation (DIC) after a Gram-negative bacterial infection. Which bacterial component is most likely responsible?

Accepted Answer

Lipid A portion of lipopolysaccharide (LPS)

Question 6

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

Accepted Answer

They bind iron more tightly than host proteins, allowing bacteria to acquire iron.

Question 7

Which enzyme produced by Streptococcus pyogenes is used therapeutically to dissolve blood clots?

Accepted Answer

Streptokinase

Question 8

A-B exotoxins have two components. Which component is responsible for binding to the host cell?

Accepted Answer

B subunit

Question 9

Which of the following best explains why Listeria monocytogenes is able to spread from cell to cell without exposure to antibodies?

Accepted Answer

It escapes the phagosome and uses actin-based motility to move directly into adjacent cells.

Question 10

Which of the following is a correct statement about the Limulus amebocyte lysate (LAL) assay?

Accepted Answer

It detects endotoxins by causing horseshoe crab amebocytes to clot in the presence of endotoxin.

Question 11

Which of the following best describes the mechanism of action of botulinum toxin?

Accepted Answer

It inhibits acetylcholine release at neuromuscular junctions, causing muscle paralysis.

Question 12

Which of the following is a function of the complement protein C3 in the classical pathway?

Accepted Answer

It increases inflammation, promotes opsonization, and leads to cytolysis.

Question 13

A patient with a viral infection produces interferon-α and interferon-β. What is the primary effect of these cytokines?

Accepted Answer

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

Question 14

Which of the following is NOT a physical or chemical barrier of innate immunity?

Accepted Answer

Antibody production by B cells

Question 15

Which of the following best explains why fever is a common response to infection with Gram-negative bacteria?

Accepted Answer

Endotoxins stimulate macrophages to release cytokines, which reset the hypothalamic thermostat.

Question 16

Which of the following is a correct sequence of events in phagocytosis?

Accepted Answer

Chemotaxis → Adherence → Ingestion → Digestion → Exocytosis

Question 17

Which of the following enzymes allows Neisseria gonorrhoeae to evade the host immune system by destroying antibodies?

Accepted Answer

IgA protease

Question 18

Which of the following is a benefit for a pathogen to survive inside host cells, such as macrophages, without being fused with lysosomes?

Accepted Answer

It avoids surveillance and attack from circulating immune cells.

Question 19

Which of the following is a correct statement about superantigens?

Accepted Answer

They cause an intense immune response by stimulating excessive cytokine release from T cells.

Question 20

Which of the following best describes the action of membrane-disrupting exotoxins such as streptolysin O?

Accepted Answer

They form protein channels in host cell membranes, leading to cell lysis.

Microbial Mechanisms of Pathogenicity and Innate Immunity

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