Question 1

Which of the following characteristics best distinguishes Staphylococcus aureus from other staphylococci in a clinical laboratory setting?

Accepted Answer

Production of coagulase

Question 2

A patient presents with a rapidly progressing, deep skin infection characterized by interconnected abscesses. Which Staphylococcus aureus-associated lesion is most likely responsible?

Accepted Answer

Carbuncle

Question 3

Which enzyme produced by Staphylococcus aureus allows it to colonize oily areas of the skin by digesting lipids?

Accepted Answer

Lipase

Question 4

A hospital patient develops a wound infection after surgery. Laboratory tests reveal a Gram-positive coccus, catalase-positive, coagulase-negative, and able to grow anaerobically with urease production and mannitol fermentation. Which species is most likely responsible?

Accepted Answer

Staphylococcus epidermidis

Question 5

Which of the following is a major virulence factor of Streptococcus pyogenes that helps it evade phagocytosis and is highly variable among strains?

Accepted Answer

M-protein

Question 6

A child develops a fever and a bright red rash after a sore throat. Which toxin is most likely responsible for these symptoms in a Streptococcus pyogenes infection?

Accepted Answer

Erythrogenic (pyrogenic) toxin

Question 7

Which of the following is NOT a typical complication of untreated Streptococcus pyogenes pharyngitis?

Accepted Answer

Otitis media

Question 8

A Gram-positive, catalase-negative, alpha-hemolytic coccus is isolated from a patient with subacute endocarditis. Which organism is most likely responsible?

Accepted Answer

Viridans group streptococcus

Question 9

Which of the following best explains why Streptococcus pneumoniae is a leading cause of bacterial pneumonia in susceptible individuals?

Accepted Answer

It forms large capsules that inhibit phagocytosis

Question 10

A newborn develops sepsis and meningitis shortly after birth. Which organism is most likely responsible, and what is the most important risk factor?

Accepted Answer

Streptococcus agalactiae; maternal vaginal colonization

Question 11

Which of the following statements about Neisseria gonorrhoeae is TRUE?

Accepted Answer

It produces IgA protease to evade mucosal immunity

Question 12

A college student living in a dormitory develops sudden fever, headache, and a petechial rash. Which organism is most likely responsible, and what is a key virulence factor?

Accepted Answer

Neisseria meningitidis; capsule

Question 13

Which laboratory test would best differentiate Streptococcus pneumoniae from other alpha-hemolytic streptococci?

Accepted Answer

Optochin sensitivity

Question 14

A patient with a prosthetic heart valve is at increased risk for subacute endocarditis following dental procedures. Which organism is most likely responsible, and what preventive measure is recommended?

Accepted Answer

Streptococcus mutans; prophylactic antibiotics

Question 15

Which of the following best describes the mechanism of methicillin resistance in MRSA?

Accepted Answer

Alteration of penicillin-binding proteins

Question 16

A patient presents with fever, vomiting, rash, and multi-organ failure after using tampons. Which toxin is most likely responsible for this syndrome?

Accepted Answer

Toxic shock syndrome toxin (TSST-1)

Question 17

Which of the following is the most appropriate initial treatment for a severe MRSA infection?

Accepted Answer

Vancomycin

Question 18

Which of the following statements about Streptococcus pneumoniae is FALSE?

Accepted Answer

It is highly contagious and spreads easily between people

Question 19

A Gram-negative diplococcus is isolated from a urethral exudate and is oxidase positive but does not ferment maltose. Which organism is most likely responsible?

Accepted Answer

Neisseria gonorrhoeae

Question 20

Which of the following best explains why Staphylococcus aureus can cause food poisoning even after food is thoroughly reheated?

Accepted Answer

Its enterotoxins are heat-stable and remain active after heating

Study Notes: Gram-Positive and Gram-Negative Cocci of Medical Importance (Staphylococcus & Streptococcus)

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