$$LD_{50} = \text{Dose at which 50\% of animals die}$$

Question 1

Which of the following best describes an opportunistic pathogen?

Accepted Answer

A microbe that does not usually cause disease but can in immunocompromised hosts.

Question 2

Which structure is NOT typically involved in microbial adherence to host tissues?

Accepted Answer

Ribosomes

Question 3

A patient develops septic shock after a bloodstream infection. Which process is most directly responsible for the dangerous drop in blood pressure?

Accepted Answer

Massive inflammation triggered by bacteria multiplying in the bloodstream

Question 4

Which of the following is a key feature shared by all AB exotoxins?

Accepted Answer

They consist of a binding (B) subunit and an activating (A) subunit.

Question 5

Why do gram-positive bacteria not produce endotoxins?

Accepted Answer

They lack an outer membrane containing lipopolysaccharide (LPS).

Question 6

Which equation correctly represents the calculation of LD50, the lethal dose that kills 50% of a test group?

Accepted Answer

$$LD_{50} = 	ext{Dose at which 50\% of animals die}$$

Question 7

Which of the following enzymes allows a pathogen to invade deeper tissues by breaking down host connective tissue?

Accepted Answer

Collagenase

Question 8

A patient with HIV is more susceptible to infections by opportunistic pathogens. This is because:

Accepted Answer

HIV inactivates one or more host resistance mechanisms.

Question 9

Which of the following is TRUE about exotoxins?

Accepted Answer

They are proteins released from the pathogen cell as it grows.

Question 10

Which property distinguishes endotoxins from exotoxins?

Accepted Answer

Endotoxins are generally less toxic and are lipopolysaccharides.

Question 11

Which of the following is a function of coagulase produced by Staphylococcus aureus?

Accepted Answer

Forms clots to wall off pathogens from immune cells.

Question 12

Which of the following is a consequence of superantigen exotoxins?

Accepted Answer

Overstimulation of the immune system leading to toxic shock syndrome.

Question 13

Which of the following is NOT a Salmonella virulence factor?

Accepted Answer

Ribosomal RNA

Question 14

Which of the following best explains attenuation in the context of vaccine development?

Accepted Answer

The decrease or loss of virulence of a pathogen, often by lab culture.

Question 15

Which of the following statements about cytolytic toxins is correct?

Accepted Answer

They degrade cytoplasmic membrane integrity, causing cell lysis and death.

Question 16

Which laboratory assay is commonly used to detect the presence of endotoxin?

Accepted Answer

Limulus amoebocyte lysate (LAL) assay

Question 17

A patient is exposed to a pathogen that produces an AB exotoxin. What is the role of the B subunit?

Accepted Answer

It binds to the host cell receptor, allowing the A subunit to enter the cell.

Question 18

Which of the following is a real-world example of a disease caused by a superantigen?

Accepted Answer

Toxic shock syndrome caused by Staphylococcus aureus

Question 19

Which of the following best describes the role of mucous membranes in colonization?

Accepted Answer

They provide a surface for microbial adherence and initial growth.

Question 20

Which of the following is a plausible reason for the attenuation of a pathogen in laboratory culture?

Accepted Answer

Virulence genes are no longer advantageous and may be lost.

Microbial Pathogenesis: Mechanisms of Infection, Virulence, and Host Interaction

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