A 36-Year-Old Man Is Admitted to the Hospital with Severe

A 36-year-old man is admitted to the hospital with severe left leg pain after suffering a minor laceration to the leg 2 days earlier.  Temperature is 39.5 C (103.1 F) and blood pressure is 85/45 mm Hg.  On physical examination, the left leg is swollen and firm with erythema of the overlying skin.  There is a small wound draining blood-tinged exudate on the left calf.  The patient is taken to the operating room immediately, and a large area of necrotic tissue is excised.  Gram stain of the necrotic tissue shows gram-positive cocci, and culture of the bacteria performed on a blood agar plate grows small colonies with a wide zone of surrounding hemolysis.  Coagulase and catalase tests are negative, and pyrrolidonyl arylamidase (PYR) test is positive.  Which of the following pathogens is most likely responsible for this patient's condition?

A) Aeromonas hydrophila
B) Clostridium perfringens
C) Staphylococcus aureus
D) Streptococcus agalactiae
E) Streptococcus pyogenes

Correct Answer:

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