Soluble group- and type-specific antigens from type III group B Streptococcus

Two soluble polysaccharide antigens of a type III group B Streptoccus were isolated from the culture medium after growth of strain M732 in a chemically defined broth supplemented with acid-hydrolyzed casein. The type- and group- specific antigens were isolated from the culture supernatant by anion-exchange chromatography with diethylaminoethyl-Sephacel. Two carbohydrate-containing peaks, which had serological reactivity with group B or type III antiserum, respectively, were eluted with a linear NaCl gradient and further purified by gel filtration. The type III polysaccharide was found to contain glucose, galactose, glucosamine, and sialic acid, whereas the group B polysaccharide contained galactose, glucosamine, and rhamnose. For the type III polysaccharide, sialic acid was shown to be the major immunodeterminant, and for the group B polysaccharide, rhamnose was the immunodominant sugar. Both the type III and group B polysaccharides were obtained in high yields without employing harsh physical or chemical treatment and both were immunologically distinct. By immunoelectrophoresis or counterimmunoelectrophoresis, type III antigen failed to react with group-specific antiserum and the group B antigen failed to react with type III antiserum.