Question 1

Which enzyme produced by Staphylococcus aureus allows it to survive treatment with beta-lactam antibiotics such as penicillin G?

Accepted Answer

Beta-lactamase

Question 2

A patient presents with a rapidly spreading, pus-producing lesion on the skin. Laboratory tests reveal Gram-positive cocci in chains, catalase-negative, and beta-hemolytic colonies. Which organism is most likely responsible?

Accepted Answer

Streptococcus pyogenes

Question 3

Which structural feature of Staphylococcus aureus helps it evade phagocytosis by binding to immunoglobulin G (IgG)?

Accepted Answer

Protein A

Question 4

A newborn develops bacteremia and meningitis shortly after birth. The causative agent is a Gram-positive coccus, catalase-negative, and beta-hemolytic, resistant to bacitracin. Which organism is most likely responsible?

Accepted Answer

Streptococcus agalactiae

Question 5

Which toxin produced by Staphylococcus aureus is responsible for the symptoms of scalded skin syndrome?

Accepted Answer

Exfoliative toxin

Question 6

Which of the following is the best method to differentiate Enterococcus from Streptococcus pneumoniae in a clinical laboratory?

Accepted Answer

Growth in bile

Question 7

A patient develops acute glomerulonephritis following a pharyngeal infection. Which immune mechanism is primarily responsible for this complication?

Accepted Answer

Deposition of antibody-bound streptococcal antigens in the glomeruli

Question 8

Which of the following best describes the hemolytic pattern of Streptococcus pneumoniae on blood agar?

Accepted Answer

Alpha-hemolysis

Question 9

A hospital outbreak of endocarditis is traced to a Gram-positive coccus that forms short chains, is catalase-negative, and is resistant to many antimicrobials. Which genus is most likely responsible?

Accepted Answer

Enterococcus

Question 10

Which enzyme produced by Streptococcus pyogenes breaks down blood clots and facilitates the spread of infection through tissues?

Accepted Answer

Streptokinase

Question 11

A child presents with a sore throat, fever, and a diffuse red rash that began on the chest and spread to the rest of the body. Which toxin is most likely responsible for the rash?

Accepted Answer

Pyrogenic toxin

Question 12

Which of the following is a major reason why hand antisepsis is critical in preventing healthcare-associated Staphylococcus infections?

Accepted Answer

Staphylococcus species are highly resistant to desiccation and can survive on surfaces

Question 13

Which of the following statements about the viridans group of streptococci is correct?

Accepted Answer

They are a common cause of dental caries

Question 14

A patient with a prosthetic heart valve develops endocarditis. Blood cultures reveal alpha-hemolytic, Gram-positive diplococci that are bile sensitive. Which organism is most likely responsible?

Accepted Answer

Streptococcus pneumoniae

Question 15

Which of the following best explains why Streptococcus pyogenes can cause rheumatic fever?

Accepted Answer

It triggers an autoimmune response against heart antigens

Question 16

Which of the following is a distinguishing feature of Staphylococcus epidermidis compared to Staphylococcus aureus?

Accepted Answer

S. epidermidis is a normal microbiota and causes opportunistic infections

Question 17

Which of the following is the primary reason why Streptococcus pneumoniae is able to cause disease in the lungs?

Accepted Answer

It has a capsule that prevents phagocytosis

Question 18

A patient with a history of intravenous drug use develops fever and a new heart murmur. Blood cultures grow Gram-positive cocci in clusters, catalase positive, and coagulase positive. Which organism is most likely responsible?

Accepted Answer

Staphylococcus aureus

Question 19

Which of the following best describes the mechanism of action of C5a peptidase produced by Streptococcus pyogenes?

Accepted Answer

It breaks down complement protein C5a, reducing leukocyte migration

Question 20

Which of the following is the most effective way to prevent neonatal infections caused by Streptococcus agalactiae?

Accepted Answer

Prophylactic use of penicillin during childbirth

Pathogenic Gram-Positive Cocci: Staphylococcus, Streptococcus, and Enterococcus

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