Question 1

Which of the following best describes the difference between ID$$_{50}$$ and LD$$_{50} in $$microbial pathogenicity?

Accepted Answer

ID$$_{50} is $$the infectious dose for 50% of a sample population, while LD$$_{50} is $$the lethal dose for 50% of a sample population.

Question 2

A patient is exposed to two toxins: botulinum toxin (LD$$_{50} = 0.03 ng/kg) $$and Salmonella toxin (LD$$_{50} = 12 mg/kg). $$Which statement is correct?

Accepted Answer

Botulinum toxin is more potent because its LD$$_{50} is $$lower.

Question 3

Which of the following is NOT a portal of entry for pathogens?

Accepted Answer

Liver

Question 4

How do bacterial capsules contribute to pathogenicity?

Accepted Answer

They impair phagocytosis by host cells.

Question 5

Which enzyme produced by bacteria digests the polysaccharides that hold cells together, facilitating tissue invasion?

Accepted Answer

Hyaluronidase

Question 6

A drug that binds mannose on human cells would most likely interfere with which step of microbial infection?

Accepted Answer

Adherence of the pathogen to host cells

Question 7

Why are biofilms significant in microbial pathogenicity?

Accepted Answer

They make bacteria more resistant to phagocytosis due to the extracellular polymeric substance (EPS).

Question 8

Which of the following best explains why the influenza vaccine does not provide long-term protection?

Accepted Answer

The influenza virus undergoes antigenic variation, altering its surface antigens.

Question 9

Which bacterial structure is responsible for resisting digestion inside phagocytes, as seen in Mycobacterium tuberculosis?

Accepted Answer

Waxy lipid (mycolic acid) in the cell wall

Question 10

What is the primary function of siderophores in bacterial pathogenicity?

Accepted Answer

To bind iron more tightly than host cells, allowing bacteria to acquire essential nutrients

Question 11

Which of the following is a characteristic of exotoxins but NOT endotoxins?

Accepted Answer

Can be converted to toxoids for vaccination

Question 12

A patient develops fever and shock after cardiac catheterization with sterile equipment washed in sterilized water. The water tested negative for bacteria. What is the most likely explanation?

Accepted Answer

The water contained endotoxins that were not removed by sterilization.

Question 13

Which of the following is a cytopathic effect of viral infection?

Accepted Answer

Formation of inclusion bodies in the cytoplasm

Question 14

Which mechanism allows Shigella and Listeria to move from one host cell to another?

Accepted Answer

Rearrangement of actin filaments in the host cytoskeleton

Question 15

Which of the following best describes the action of A-B exotoxins?

Accepted Answer

The B component binds to the host cell, and the A component exerts the toxic effect.

Question 16

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

Accepted Answer

It uses horseshoe crab blood cells to detect endotoxins by clot formation.

Question 17

Which of the following is a portal of exit commonly used by pathogens?

Accepted Answer

Respiratory tract via coughing and sneezing

Question 18

How can lysogeny turn a normally harmless strain of E. coli into a pathogen?

Accepted Answer

By incorporating a prophage that carries toxin genes

Question 19

Which of the following is NOT a mechanism by which bacteria avoid destruction by phagocytes?

Accepted Answer

Secreting siderophores

Question 20

Which of the following best explains the difference between food infection and food intoxication?

Accepted Answer

Food infection is caused by microbial growth in the host, while food intoxication is caused by ingestion of preformed toxins.

Microbial Mechanisms of Pathogenicity: Study Notes

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