An alpha-haemolytic diplococcal isolate from CSF of a child with meningitis must be distinguished from viridans streptococci. The result that confirms Streptococcus pneumoniae is:

• A Growth on 6.5% sodium chloride broth
• B Positive PYR test
• C Hydrolysis of hippurate
• D Bile solubility and optochin susceptibility ✓

Explanation

Pneumococci are lysed by bile salts because their autolytic enzyme LytA is activated, and they are inhibited by optochin (ethylhydrocupreine hydrochloride); viridans streptococci are negative for both. Growth in 6.5% NaCl identifies group B enterococci, hippurate hydrolysis identifies Group D Streptococcus, and the PYR test points to Enterococcus or S. pyogenes. Bile solubility plus optochin sensitivity is the classic paired confirmation for pneumococcus.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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