Multiple polysaccharide antigens of group B streptococcus, type Ia: emphasis on a sialic acid type-specific polysaccharide

Group B streptococci, type Ia (strain 090/14/4), were subjected to sequential extraction procedures and the various extracts were fractionated by a combination of DEAE-cellulose chromatography and gel-filtration. Three major antigens were isolated: the conventional group-specific and type-specific carbohydrates and an acidic polysaccharide consisting of galactose, glucose, glucosamine, and sialic acid. Immunochemical data suggest that the acidic antigen, with the exception of the immunodominant sialic acid, is structurally similar to the conventional pH 2.0 extracted type-specific antigen. Removal of the terminal sialic acid residues from the acidic antigen by mild acid hydrolysis resulted in a residual polymer which was chemically and immunologically analogous to the type-specific carbohydrate. Precipitin analysis focused attention to the cross-reactivity between thia acidic antigen and anti-types Ib, Ic, and III sera.