Group B streptococcal C protein-associated antigens: association with neonatal sepsis.

The c protein (Ibc) of group B streptococci (GBS) is associated with at least four antigens (alpha, beta, gamma, delta). To assess the virulence potential of these antigens, 255 GBS isolates recovered from septic neonates, healthy neonates, and pregnant women were serotyped and surveyed for reactivity with sera to c protein and the four associated antigens. A radioimmunoassay using intact bacteria was used to detect the GBS antigens. In contrast to earlier reports, most (66%) of the type III strains expressed the c protein. Except for the gamma antigen, none of the other c protein-associated antigens showed an increased association with pathogenic strains independent of the polysaccharide antigens. The gamma antigen was expressed by 15 of 41 c protein-positive early-onset strains and by 4 of 38 c protein-positive late-onset strains (P = .007). This association was independent of the type-specific antigen, suggesting a potential role for the gamma antigen as a virulence factor in GBS strains causing early-onset sepsis.