Pus aspirated from a boil shows Gram-positive cocci in clusters. A single laboratory test performed on the isolate reliably separates this organism from Streptococcus pyogenes before any further workup. Which test is this?

• A Coagulase test
• B Oxidase test
• C Catalase test ✓
• D Optochin susceptibility test

Explanation

Staphylococci produce catalase and streptococci do not, so bubbling on adding hydrogen peroxide confirms Staphylococcus. The coagulase test then separates S. aureus from coagulase-negative species, but the first branching point between staphylococci and streptococci is catalase. Oxidase is used for gram-negative rods and optochin for pneumococci, so neither applies here.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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