A 25-year-old man presents with acute pharyngitis, tender anterior cervical lymphadenopathy, fever, and tonsillar exudate. A throat swab culture on sheep blood agar shows small beta-hemolytic colonies. The isolate is bacitracin-sensitive and PYR test positive. The organism is most likely classified under which Lancefield group?

• A Group C
• B Group B
• C Group D
• D Group A ✓

Explanation

Bacitracin sensitivity and PYR positivity are key identifying features of Streptococcus pyogenes (Group D beta-hemolytic streptococcus, GAS). Bacitracin sensitivity distinguishes GAS from other beta-hemolytic streptococci. PYR (L-pyrrolidonyl arylamidase) positivity is a rapid confirmatory test for GAS. Group B streptococcus is bacitracin-resistant, CAMP test positive, and PYR-negative.

Reference: Forbes, Sahm, and Bailey Diagnostic Microbiology, 15th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.