Question 1

Which of the following best describes an opportunistic pathogen?

Accepted Answer

A microbe that can only cause disease in the absence of normal host resistance.

Question 2

Which structure is commonly used by bacteria to adhere to host tissues during the initial stages of infection?

Accepted Answer

Pili (fimbriae)

Question 3

A patient develops a systemic infection after bacteria multiply in the bloodstream. What is the correct term for this condition?

Accepted Answer

Septicemia

Question 4

Which of the following statements about virulence factors is CORRECT?

Accepted Answer

Virulence factors are substances or strategies that help pathogens establish infection.

Question 5

The LD$_{50}$ (lethal dose 50) is used to measure virulence. What does a lower LD$_{50}$ value indicate?

Accepted Answer

The pathogen is more virulent.

Question 6

Why do gram-positive bacteria NOT produce endotoxins?

Accepted Answer

They lack a lipopolysaccharide layer in their cell envelope.

Question 7

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

Accepted Answer

They consist of two subunits: one for binding and one for enzymatic activity.

Question 8

Which enzyme produced by Staphylococcus aureus helps the pathogen evade the immune system by forming clots?

Accepted Answer

Coagulase

Question 9

A patient with a compromised immune system develops pneumonia from a normally harmless microbe. This is an example of:

Accepted Answer

Opportunistic infection

Question 10

Which of the following best describes the action of cytolytic (cytotoxin) exotoxins?

Accepted Answer

They degrade cytoplasmic membrane integrity, causing cell lysis.

Question 11

Which of the following is TRUE regarding endotoxins?

Accepted Answer

They are part of the lipopolysaccharide layer of gram-negative bacteria.

Question 12

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

Accepted Answer

Limulus amoebocyte lysate (LAL) assay

Question 13

Which of the following is a reason why attenuation is important in vaccine development?

Accepted Answer

Attenuated pathogens can stimulate immunity without causing severe disease.

Question 14

Which of the following is a function of hyaluronidase as a virulence factor?

Accepted Answer

It breaks down host connective tissue, facilitating invasion.

Question 15

A patient develops toxic shock syndrome (TSS) after a localized Staphylococcus aureus infection. Which type of exotoxin is responsible?

Accepted Answer

Superantigen toxin

Question 16

Which of the following best explains why virulence often decreases when a pathogen is grown in laboratory culture?

Accepted Answer

The pathogen adapts to the laboratory environment and loses traits needed for infection.

Question 17

Which of the following is NOT a typical property of exotoxins compared to endotoxins?

Accepted Answer

Exotoxins are part of the outer membrane of gram-negative bacteria.

Question 18

Which of the following is a real-world example of an AB exotoxin affecting the nervous system?

Accepted Answer

Botulinum toxin causing flaccid paralysis

Question 19

Which of the following best describes the difference between infection and disease?

Accepted Answer

Infection is the growth/establishment of a pathogen in a host; disease is the damage caused to the host.

Question 20

Which of the following is a major function of pathogenicity islands in Salmonella species?

Accepted Answer

They encode clusters of virulence genes that enhance pathogenicity.

25. Human-Pathogen Interactions, Virulence, and Bacterial Toxins

Study Guide - Practice Questions