Escherichia coli K1 Capsular Polysaccharide Associated with Neonatal Meningitis

Examination of 77 strains of Escherichia coli from the cerebrospinal fluid of neonates with meningitis revealed 65 (84 per cent) with the capsular (K1) polysaccharide. The Esch. coli K1 capsular antigen has been shown to be immunochemically identical to the meningococcal Group B polysaccharide. These cerebrospinal-fluid Esch. coli K1 strains were associated with at least seven different somatic (O) and three flagella (H) antigens. In contrast, Esch. coli K1 strains were found in 14 of 36 (39 per cent) blood cultures of neonates without meningitis and in approximately 15 per cent of blood, urine and stool cultures from adults and rectal cultures from infants. The mean median lethal dose in a mucin-enhanced mouse model for 31 neonatal cerebrospinal-fluid K1 isolates was 168 organisms. In contrast, the median lethal dose for 10 neonatal non-K1 isolates was 58,000 and was greater than 10,000 organisms for six non-K1 enteropathogenic strains and five K1 strains isolated from normal infant stools. The high prevalence of the K1 antigen in neonatal meningitis suggests that this capsular polysaccharide is related to Esch. coli invasiveness in the newborn. A protective effect of anti-capsular antibody in a mouse model suggests that immunity to neonatal Esch. coli K1 meningitis may be mediated by serum antibodies. (N Engl J Med 290:1216–1220, 1974)