A 25-year-old man develops a painful, swollen, erythematous skin wound after a compound fracture. Gram stain of wound discharge shows Gram-positive cocci in chains and Gram-positive rods. The isolate grows as beta-haemolytic colonies that are catalase-negative and PYR-positive. Which organism is this?

• A Streptococcus agalactiae (Group B)
• B Streptococcus pneumoniae
• C Enterococcus faecalis
• D Streptococcus pyogenes (Group A) ✓

Explanation

PYR (L-pyroglutamyl-beta-naphthylamide) hydrolysis is a rapid test for Group A Streptococcus (S. pyogenes), which is PYR-positive. Group B Streptococcus and Enterococcus are PYR-negative. S. pneumoniae is alpha-haemolytic. The Gram-positive rods are likely contaminants or skin flora (Corynebacterium), while the clinical picture fits S. pyogenes wound infection with potential for necrotizing fasciitis.

Reference: Jawetz, Melnick, and Adelberg's Medical Microbiology, 28th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.