Question 1

Which characteristic of Mycobacterium tuberculosis allows it to evade destruction by macrophages after being phagocytized in the alveoli?

Accepted Answer

Presence of waxy mycolic acids in the cell wall

Question 2

A patient presents with a black eschar on the skin after handling animal hides. Which organism is most likely responsible, and what is the key virulence factor?

Accepted Answer

Bacillus anthracis; capsule and exotoxins

Question 3

Which of the following best explains why botulism is not treated with antibiotics?

Accepted Answer

The illness is caused by a preformed toxin, not by bacterial growth

Question 4

A patient develops muscle rigidity and spasms after a puncture wound. Which toxin is responsible, and what is its mechanism?

Accepted Answer

Tetanus toxin; inhibits release of gamma aminobutyric acid (GABA)

Question 5

Which laboratory test would best distinguish Staphylococcus aureus from Streptococcus pyogenes in a wound sample?

Accepted Answer

Catalase test

Question 6

A hospital patient develops diarrhea after a course of antibiotics. Which organism is most likely responsible, and what is the recommended first step in treatment?

Accepted Answer

Clostridium difficile; discontinue antibiotics

Question 7

Which of the following best describes the mechanism of action of Staphylococcus aureus Protein A?

Accepted Answer

It binds to the constant region of antibodies, inhibiting phagocytosis

Question 8

A child presents with large, fluid-filled blisters that rupture and form yellowish crusts around the mouth. Which condition is most likely, and what is a possible complication if caused by Streptococcus pyogenes?

Accepted Answer

Impetigo; acute glomerulonephritis

Question 9

Which of the following is a key reason why Staphylococcus aureus food poisoning can occur even after food is reheated to 100°C?

Accepted Answer

The enterotoxins are heat-stable and resist boiling

Question 10

A patient with a history of blunt trauma develops rapidly spreading tissue necrosis and systemic symptoms. Which organism is most likely, and what is the primary treatment?

Accepted Answer

Streptococcus pyogenes; surgical debridement and intravenous antibiotics

Question 11

Which of the following best explains why MRSA is a significant concern in hospital settings?

Accepted Answer

It is resistant to multiple antibiotics and can spread easily among patients

Question 12

Which of the following is the most effective way to prevent Clostridium perfringens food poisoning?

Accepted Answer

Proper handling, cooking, and refrigeration of foods

Question 13

A patient receives a Mantoux tuberculin skin test. Which of the following could cause a false-positive result?

Accepted Answer

Prior vaccination with BCG

Question 14

Which of the following best describes the appearance of Streptococcus pyogenes under the microscope?

Accepted Answer

Chains of cocci

Question 15

Which of the following is a recommended protocol for tetanus vaccination in adults?

Accepted Answer

One dose every 10 years

Question 16

Which of the following best explains why Clostridium difficile infections are associated with prior antibiotic use?

Accepted Answer

Antibiotics disrupt normal gut microbiota, allowing C. difficile to proliferate

Question 17

A patient with a wound infection is found to have coagulase-positive, catalase-positive, Gram-positive cocci in clusters. Which organism is most likely?

Accepted Answer

Staphylococcus aureus

Question 18

Which of the following is a major concern with the use of the anthrax vaccine in the general population?

Accepted Answer

It requires multiple injections and is only approved for at-risk adults

Question 19

Which of the following best describes the pathogenesis of acne caused by Propionibacterium acnes?

Accepted Answer

It consumes sebum and secretes enzymes that damage hair follicles, leading to inflammation

Question 20

Which of the following best explains why necrotizing fasciitis can progress rapidly and require amputation?

Accepted Answer

Bacterial proteases destroy host tissues and prevent immune cell migration

Gram-Positive Bacterial Diseases of the Skin and Related Systems

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