A Gram stain from a pus swab shows Gram-positive cocci in clusters. Which single laboratory test best separates this organism from Streptococcus pyogenes?

• A Coagulase test
• B Catalase test ✓
• C Optochin susceptibility
• D Bile esculin hydrolysis

Explanation

Staphylococcus species produce the enzyme catalase, which splits hydrogen peroxide into water and oxygen, giving immediate effervescence; streptococci lack catalase and show no bubbles. This is the first step in identifying Gram-positive cocci. Coagulase then separates S. aureus from coagulase-negative staphylococci, so it is a second-line test here. Optochin and bile esculin are used among streptococci and enterococci respectively, not to separate staphylococci from streptococci.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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