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. Why?

Accepted Answer

Gram-positive bacteria are more resistant to desiccation and high salt concentrations

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 its most common causative agent?

Accepted Answer

Swimmer's ear; Pseudomonas aeruginosa

Question 5

A 4-year-old girl has a rash with yellow scabs around her nose. 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 culture of blister fluid be negative?

Accepted Answer

Staphylococcal Scalded Skin Syndrome; the toxin causes symptoms but bacteria are not present in the blisters

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 that 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?

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 and produce toxins 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

Which of the following is a common prevention strategy for conjunctivitis outbreaks in clinical settings?

Accepted Answer

Strict hand hygiene and disinfection of shared equipment

Question 15

Which bacteria are characterized as group A beta-hemolytic?

Accepted Answer

Streptococcus pyogenes

Question 16

Which of the following best explains why blood cultures may be negative in toxin-mediated diseases such as toxic shock syndrome?

Accepted Answer

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

Question 17

Which of the following is a distinguishing feature of Pseudomonas aeruginosa infections?

Accepted Answer

Production of blue-green pigment (pyocyanin)

Question 18

Which of the following best describes a vesicle?

Accepted Answer

A small, fluid-filled blister

Question 19

Which of the following is a common misconception about the transmission of conjunctivitis?

Accepted Answer

It can be spread by contaminated hands, towels, or equipment

Microbiology Study Guide: Skin and Soft Tissue Infections

Study Guide - Practice Questions

Study Guide - Flashcards