Question 1

Which of the following characteristics best distinguishes Staphylococcus aureus from Staphylococcus epidermidis?

Accepted Answer

Coagulase production

Question 2

A patient presents with a rapidly progressing infection of the subcutaneous tissue, resulting in tissue necrosis and systemic inflammation. Laboratory tests reveal a beta-hemolytic, catalase-negative, Gram-positive cocci that is bacitracin sensitive. Which organism is most likely responsible?

Accepted Answer

Streptococcus pyogenes

Question 3

Which virulence factor produced by Staphylococcus aureus is primarily responsible for the formation of fibrin clots that protect the bacteria from phagocytosis?

Accepted Answer

Coagulase

Question 4

A newborn develops sepsis and meningitis within the first week of life. The causative agent is a beta-hemolytic, catalase-negative, Gram-positive cocci isolated from the mother’s genital tract. Which organism is most likely responsible?

Accepted Answer

Streptococcus agalactiae

Question 5

Which of the following best explains why toxic shock syndrome caused by Staphylococcus aureus can lead to cardiovascular collapse and kidney failure?

Accepted Answer

Release of a superantigen toxin that triggers a massive T cell and inflammatory response

Question 6

Which test result would help differentiate Enterococcus faecalis from Streptococcus bovis in a clinical laboratory?

Accepted Answer

Growth in 6.5% NaCl

Question 7

A Gram-positive, catalase-positive, coagulase-negative cocci is isolated from a wound infection. It is DNase negative, unable to ferment mannitol, and grows in 7.5% NaCl. Which organism is most likely?

Accepted Answer

Staphylococcus epidermidis

Question 8

Which of the following is a distinguishing feature of Streptococcus pneumoniae compared to Streptococcus pyogenes?

Accepted Answer

Alpha hemolysis and optochin sensitivity

Question 9

A young, sexually active female presents with a urinary tract infection. The causative agent is a Gram-positive, catalase-positive, coagulase-negative cocci that is part of the normal flora of the genitourinary tract. Which organism is most likely responsible?

Accepted Answer

Staphylococcus saprophyticus

Question 10

Which of the following best describes the mechanism by which Streptococcus pyogenes causes rheumatic fever?

Accepted Answer

Immune-mediated cross-reactivity between bacterial and host antigens

Question 11

Which of the following statements about MRSA and VRSA is correct?

Accepted Answer

They are resistant to nearly all antibiotics, not just methicillin and vancomycin

Question 12

A patient develops food poisoning with severe but short-lived diarrhea and vomiting after eating contaminated food. The causative agent is a Gram-positive cocci that produces enterotoxin A. What is the mechanism of action of this toxin?

Accepted Answer

Acts as a superantigen, stimulating massive T cell response in the intestine

Question 13

Which of the following organisms is most associated with the formation of dental caries due to lactic acid fermentation?

Accepted Answer

Streptococcus salivarius

Question 14

A laboratory is testing a Gram-positive cocci for hemolysis, esculin hydrolysis, and salt tolerance. The organism is gamma hemolytic, esculin hydrolysis positive, and grows in 6.5% NaCl. Which organism is most likely?

Accepted Answer

Enterococcus faecalis

Question 15

Which of the following best explains why Staphylococcus aureus is often associated with pus formation in skin infections?

Accepted Answer

Production of leukocidin, which destroys phagocytic cells

Question 16

A Gram-positive, catalase-negative cocci is isolated from a patient with endocarditis. The organism is alpha hemolytic, esculin hydrolysis positive, and unable to grow in 6.5% NaCl. Which organism is most likely?

Accepted Answer

Streptococcus bovis

Question 17

Which of the following is a key difference between Micrococcus and Staphylococcus species?

Accepted Answer

Micrococcus is coagulase negative and grows in tetrads; Staphylococcus grows in clusters

Question 18

A patient with a recent influenza A infection develops a severe soft-tissue infection with bacteremia and acute respiratory distress syndrome (ARDS). The causative agent is a beta-hemolytic, catalase-negative cocci. Which syndrome is most likely present?

Accepted Answer

Streptococcal Toxic Shock-like Syndrome

Question 19

Which of the following best describes the role of the M-protein in Streptococcus pyogenes infections?

Accepted Answer

Acts as a superantigen, recruiting massive numbers of T cells

Question 20

Which of the following is true regarding the hemolytic patterns of Streptococcus species?

Accepted Answer

Streptococcus pyogenes is beta hemolytic, Streptococcus pneumoniae is alpha hemolytic

Micrococcaceae and Streptococcaceae: Structure, Pathogenicity, and Clinical Relevance

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