Question 1

Which of the following best describes an opportunistic pathogen?

Accepted Answer

A pathogen that is part of the normal flora and causes disease only when it gains access to other tissue sites or the host is immunocompromised.

Question 2

According to Koch’s postulates, which step is necessary to confirm that a microorganism causes a specific disease?

Accepted Answer

The cultured microorganism must cause disease when re-introduced into a healthy organism.

Question 3

During which stage of infectious disease is the disease most severe and has characteristic signs and symptoms?

Accepted Answer

Period of illness

Question 4

A patient presents with severe diarrhea described as 'rice-water stool.' Which pathogen is most likely responsible?

Accepted Answer

Vibrio cholerae

Question 5

Which mechanism allows Neisseria gonorrhoeae to escape the adaptive immune response?

Accepted Answer

Phase variation of pilin genes resulting in altered pilin amino acid sequences

Question 6

Staphylococcus aureus is able to extract iron from the host using which of the following systems?

Accepted Answer

Isd system for extracting heme from hemoglobin

Question 7

Methicillin resistance in Staphylococcus aureus is primarily mediated by which gene?

Accepted Answer

mecA

Question 8

Which equation best represents the catalase reaction used by Staphylococcus aureus to resist oxidative burst killing?

Accepted Answer

$$2H_2O_2 \rightarrow 2H_2O + O_2$

Question 9

Which of the following is a major nosocomial pathogen that can cause surgical site infections, pneumonia, and endocarditis?

Accepted Answer

Staphylococcus aureus

Question 10

The accessory gene regulator (agr) system in Staphylococcus aureus is an example of which bacterial communication mechanism?

Accepted Answer

Quorum sensing

Question 11

Which of the following best explains why sickle-cell disease confers resistance to malaria?

Accepted Answer

Sickle cells lyse before Plasmodium can replicate to high numbers, allowing the immune system to catch up.

Question 12

Which of the following drugs is used to treat latent Mycobacterium tuberculosis infection?

Accepted Answer

Isoniazid

Question 13

Yersinia pestis resists phagocytosis by macrophages through which mechanism?

Accepted Answer

Depolymerizing the actin cytoskeleton via Yop effector proteins

Question 14

Which of the following is a vector for Plasmodium species causing malaria?

Accepted Answer

Female Anopheles mosquito

Question 15

Which stage of Plasmodium life cycle occurs first in the human host after a mosquito bite?

Accepted Answer

Sporozoite invasion of hepatocytes

Question 16

Which of the following is a characteristic symptom of cutaneous leishmaniasis?

Accepted Answer

Lesions with raised edges and a central crater ('volcano' appearance)

Question 17

Which form of Leishmania is found in humans and is characterized by an oval shape with rudimentary flagella?

Accepted Answer

Amastigote

Question 18

Which of the following treatments is most effective against Yersinia pestis infection?

Accepted Answer

Gentamicin and fluoroquinolones

Question 19

African sleeping sickness is caused by Trypanosoma brucei and transmitted by which vector?

Accepted Answer

Tsetse fly

Question 20

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

Accepted Answer

It increases cAMP production, leading to phosphorylation of the CFTR channel and secretion of chloride into the gut lumen.

Bacterial Pathogenesis and Selected Human Pathogens

Study Guide - Practice Questions