A throat isolate is beta-haemolytic and catalase negative. It shows a zone of inhibition around a bacitracin disc and gives a positive PYR test. The Lancefield group of this organism is:
- A Group C
- B Group B
- C Group A ✓
- D Group D
Correct answer: C. Group A
Explanation
Bacitracin sensitivity identifies Streptococcus pyogenes as Lancefield Group C, since it is susceptible while most other beta-haemolytic streptococci resist bacitracin. The positive PYR (L-pyrrolidonyl arylamidase) test supports Group C or Enterococcus, but enterococci are not beta-haemolytic typically and belong to Group D. Group B streptococci are bacitracin resistant and CAMP positive. Rapid latex agglutination for the group C carbohydrate antigen confirms the identification.
Reference: Ananthanarayan and Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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