Immunochemical studies on the cell-wall antigen of group B streptococcus, type Ib.

A polysaccharide antigen of group B streptococcus type Ib was extracted from sodium dodecyl sulphate-treated cell walls by trichloroacetic acid. In crossed immunoelectrophoresis the polymer reacted with specific antisera to serotypes Ia, Ib and Ic of group B streptococci and with commercial grouping antiserum to give one precipitin line. However, the antigen did not react with antisera to types II and III. The evidence suggests that this polymer confers the group specificity to type Ib of group B streptococci. The polysaccharide, after purification on DEAE-cellulose, was shown to consist of rhamnose, glucosamine, galactose, glucose, sialic acid and a trace of phosphorus.