A Gram stain from a pus swab shows Gram-positive cocci in clusters. Which single rapid biochemical test will differentiate this isolate from Streptococcus pyogenes?

• A Optochin disc test
• B Coagulase test
• C Bacitracin disc test
• D Catalase test ✓

Explanation

Catalase decomposes hydrogen peroxide into water and oxygen, seen as bubbling. Staphylococci are catalase positive because they are aerobes with cytochrome systems, while streptococci lack catalase and are catalase negative. This is the first step in differentiating the two genera on Gram-positive cocci. Coagulase then separates S. aureus from coagulase-negative species, while bacitracin and optochin tests work within the streptococci, so they cannot separate Staphylococcus from Streptococcus.

Reference: Ananthanarayan and Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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