A sputum isolate of Gram-positive diplococci is confirmed as Streptococcus pneumoniae when a suspension of the organism becomes clear within minutes after addition of sodium deoxycholate. This bile solubility results from:

• A Disruption of the capsule by detergent action
• B Lysis through complement activation by the alternative pathway
• C Inhibition of peptidoglycan cross-linking by the bile salt
• D Activation of the autolytic enzyme LytA amidase ✓

Explanation

Pneumococci carry the autolysin LytA, an amidase normally held in check during logarithmic growth. Bile salts activate LytA, which degrades the peptidoglycan of the cell wall and causes the suspension to clear. Viridans streptococci lack this enzyme and remain turbid, which is why bile solubility and optochin susceptibility separate the two. Capsule disruption alone would not dissolve the organism.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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