Question 1

Which of the following factors in perspiration discourages microbial growth on the skin?

Accepted Answer

Presence of lysozyme and high salt concentration

Question 2

Normal skin microbiota are more likely to be Gram-positive than Gram-negative. What is the main reason for this?

Accepted Answer

Gram-positive bacteria are more resistant to desiccation due to their thick peptidoglycan layer.

Question 3

Which of the following best describes the difference between an exanthem and an enanthem?

Accepted Answer

Exanthem is a rash on the skin; enanthem is a rash on mucous membranes.

Question 4

A patient presents with a red, swollen ear canal after swimming in a lake. What is the colloquial name for this condition, and what is the most common causative agent?

Accepted Answer

Swimmer's ear; Pseudomonas aeruginosa

Question 5

A 4-year-old girl presents with a rash around her nose, small pustules, and yellow scabs. The bacteria are catalase-negative, Gram-positive cocci in chains. What is the diagnosis and causative agent?

Accepted Answer

Impetigo; Streptococcus pyogenes

Question 6

A pediatric patient is diagnosed with SSSS. What does SSSS stand for, and why might a microbiological culture of blister fluid be negative?

Accepted Answer

Staphylococcal Scalded Skin Syndrome; the toxin is responsible for symptoms, not the bacteria in the blister fluid.

Question 7

Why do some strains of Streptococcus pyogenes cause necrotizing fasciitis ('flesh-eating disease'), while others do not?

Accepted Answer

Some strains produce exotoxins and enzymes that destroy tissue rapidly.

Question 8

Which test is used to identify Staphylococcus aureus, and what is the principle behind it?

Accepted Answer

Coagulase test; S. aureus produces coagulase, which clots plasma.

Question 9

Why is mannitol salt agar considered a selective medium for Staphylococcus aureus?

Accepted Answer

It contains 7.5% NaCl, which inhibits most bacteria except salt-tolerant Staphylococcus species.

Question 10

A hospitalized patient develops an infection with blue-green pus and a grapelike odor. What is the most likely causative agent, and how might the infection have been acquired?

Accepted Answer

Pseudomonas aeruginosa; acquired from contaminated hospital equipment or surfaces.

Question 11

A 12-year-old diabetic girl using an insulin pump develops fever, low blood pressure, abdominal pain, and erythroderma. She rarely changes her needle-insertion site. Blood cultures are negative. What is the probable cause of her symptoms?

Accepted Answer

Toxin-mediated Staphylococcus aureus infection (toxic shock syndrome)

Question 12

A teenage male with influenza develops respiratory distress, fever, rash, and low blood pressure. S. aureus is isolated from his respiratory secretions. What is the relationship between his symptoms and the etiological agent?

Accepted Answer

S. aureus can cause a superinfection following influenza, leading to toxic shock syndrome.

Question 13

Which of the following best describes a pustule?

Accepted Answer

A small, elevated, pus-filled lesion

Question 14

How are most cases of conjunctivitis transmitted, and what is a key prevention strategy?

Accepted Answer

Direct contact; frequent handwashing and avoiding touching the eyes

Question 15

Which of the following is a characteristic of group A beta-hemolytic Streptococcus?

Accepted Answer

It produces clear zones of hemolysis on blood agar due to complete lysis of red blood cells.

Question 16

Which of the following best explains why S. aureus can cause toxic shock syndrome even when blood cultures are negative?

Accepted Answer

The disease is mediated by toxins, not by the presence of bacteria in the blood.

Question 17

Which of the following is NOT a typical function of the skin's normal microbiota?

Accepted Answer

Causing systemic infections under normal conditions

Microbiology: Skin and Soft Tissue Infections – Study Guidance

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