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

Question 1

Which of the following best describes an opportunistic pathogen?

Accepted Answer

A microorganism that only causes disease when the host's defenses are compromised.

Question 2

Which term refers to the dose of a pathogen required to kill 50% of a test population?

Accepted Answer

LD50

Question 3

A patient develops a skin infection after a minor cut. Which portal of entry did the pathogen most likely use?

Accepted Answer

Skin

Question 4

Which of the following is NOT a common mechanism by which pathogens adhere to host tissues?

Accepted Answer

Flagella

Question 5

Biofilms are important in pathogenesis because they:

Accepted Answer

Protect bacteria from host immune responses and antibiotics.

Question 6

Which enzyme produced by bacteria helps them penetrate host tissues by breaking down hyaluronic acid?

Accepted Answer

Hyaluronidase

Question 7

A bacterial pathogen is able to avoid phagocytosis by producing a capsule. This is an example of:

Accepted Answer

Physical barrier to host defenses

Question 8

Which of the following best describes antigenic variation?

Accepted Answer

The ability of a pathogen to change its surface proteins to evade the immune system.

Question 9

A patient is infected with a bacterium that produces exotoxins. Which of the following statements is TRUE about exotoxins?

Accepted Answer

Exotoxins are proteins that are secreted by bacteria and can be highly toxic.

Question 10

Which equation would you use to calculate the LD50 of a toxin in an experimental setting?

Accepted Answer

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

Question 11

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

Accepted Answer

Exotoxins are secreted by living bacteria, while endotoxins are released when bacteria die.

Question 12

A patient is exposed to diphtheria toxin. Which mechanism does this exotoxin use to harm host cells?

Accepted Answer

It inhibits protein synthesis by inactivating elongation factor 2.

Question 13

Which of the following is an example of a cytopathic effect (CPE) caused by a virus?

Accepted Answer

Cell rounding and detachment from the substrate.

Question 14

Which portal of exit is most commonly used by respiratory pathogens?

Accepted Answer

Saliva and respiratory droplets

Question 15

A bacterial pathogen produces collagenase. What is the role of this enzyme in infection?

Accepted Answer

It breaks down collagen in connective tissue, allowing the pathogen to spread.

Question 16

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

Accepted Answer

They bind and sequester iron from the host, aiding bacterial growth.

Question 17

A patient is infected with a virus that evades the immune system by rapidly changing its surface antigens. This is an example of:

Accepted Answer

Antigenic variation

Question 18

Which of the following is TRUE about superantigens?

Accepted Answer

They cause excessive activation of the immune system, leading to toxic shock.

Question 19

Which of the following is the best definition of an antitoxin?

Accepted Answer

A substance that neutralizes toxins produced by pathogens.

Question 20

A patient is exposed to both exotoxins and endotoxins. Which of the following statements correctly compares their characteristics?

Accepted Answer

Exotoxins are generally more potent and specific in their action than endotoxins.

Microbial Mechanisms of Pathogenicity: Study Notes

Study Guide - Practice Questions