A neonate develops necrotizing enterocolitis. Blood culture grows S. agalactiae (Group B Streptococcus). The virulence factor most critical for this organism to resist phagocytosis in the neonatal bloodstream is:

• A Protein A binding IgG Fc region
• B Beta-hemolysin (CAMP factor)
• C Polysaccharide capsule containing sialic acid residues ✓
• D C5a peptidase cleaving complement

Explanation

GBS polysaccharide capsule containing terminal sialic acid residues mimics host sialoglycoproteins, inhibiting complement deposition by recruiting factor H (a complement regulatory protein) and preventing alternative pathway activation; neonates lack maternal antibodies against type-specific GBS capsular polysaccharides, explaining their susceptibility. Protein A (IgG Fc binding) is a Staphylococcus aureus virulence factor. CAMP factor (beta-hemolysin) enhances hemolysis in the presence of S. aureus but is not the primary anti-phagocytic mechanism. C5a peptidase is also a GBS virulence factor but is less critical than the capsule.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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