A 5-day-old term neonate presents with fever, poor feeding, and seizures. CSF shows gram-negative bacilli. Blood and CSF cultures grow Escherichia coli. The E. coli strain most strongly associated with neonatal meningitis characteristically possesses which antigen?

• A K1 capsular antigen ✓
• B O157 somatic antigen
• C H7 flagellar antigen
• D P fimbrial antigen

Explanation

The K1 capsular antigen, structurally identical to the polysialic acid capsule of group A Neisseria meningitidis, is carried by the majority of E. coli strains causing neonatal meningitis. Its sialic acid content mimics neural tissue antigens and impairs complement-mediated killing, permitting survival in blood and CSF. The O157:H7 combination defines an enterohemorrhagic strain and P fimbriae are uropathogenic determinants.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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