A blood culture isolate shows beta-hemolysis, Lancefield group B antigen, positive CAMP test, and hydrolysis of hippurate. Which virulence factor of this organism is most important for neonatal meningitis?

• A M protein (surface protein)
• B Sialic acid-rich polysaccharide capsule (type III) ✓
• C Pyrogenic exotoxins (SPE A, B, C)
• D Protein A (immunoglobulin Fc receptor)

Explanation

The isolate is Streptococcus agalactiae (GBS, Group B Streptococcus). In neonatal meningitis, the type III polysaccharide capsule is the key virulence factor — its sialic acid residues mimic host polysialic acid, impair complement activation, and resist opsonophagocytosis. Type III GBS accounts for ~60% of neonatal meningitis and late-onset disease. M protein is the key virulence factor of GBS, not GAS. Pyrogenic exotoxins are produced by S. pyogenes (GAS). Protein A is a virulence factor of S. aureus.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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