THE Ibc PROTEIN FRACTION OF GROUP B STREPTOCOCCI: CHARACTERIZATION OF PROTEIN ANTIGENS EXTRACTED BY HC1

Abstract
The Ibc protein fraction of group B streptococci was prepared by HCl extraction of the type Ic strains A909 and 335. The fraction from strain A909 contained 2 protein antigens (.alpha.A909 and .beta.A909) that could be separated by ion-exchange chromatography and isoelectric focusing. The 335 extract contained the .alpha. (.alpha.335) antigen, but not the .beta. antigen. The .alpha.335 antigen was purified by similar procedures. The .beta.A909 antigen had a MW of several hundred thousands, was immunogenic in rabbits and dissociated into several polypeptides on SDS-PAGE [sodium dodecyl sulfate polyaccylamide gel electrophoresis]. Polypeptides with sub-unit MW corresponding to 70,000; 45,000; and 23,000 daltons showed antigenic activity. The .alpha.335 antigen had a MW of .apprx. 75,000 daltons as judged from gel filtration and SDS-PAGE. The antigen was immunogenic in rabbits. In contrast, the .alpha.A909 antigen showed neither protein lines on SDS-PAGE, nor immunogenicity in rabbits. However, the 2 .alpha. antigens showed serological crossreactivity in tests with the anti-.alpha.335 serum.