The Ibc proteins of group B streptococci: trypsin extracted alpha antigen and detection of the alpha and beta antigens.

In order to study the antigen composition of different group B streptococcal strains as regards the Ibc proteins alpha and beta, different methods for extraction were compared. Bacteria of the serotype Ic strains A909 and 335 were treated with HCl, urea, Triton-X-100, EDTA, or trypsin. Extraction with HCl was most efficient for the preparation of the beta antigen; trypsin extraction for the alpha antigen. The trypsin-extracted alpha A909 and alpha 335 antigens showed similar characteristics. Double-diffusion analysis showed a reaction of identity; on Sephacryl:S-200 filtration both appeared with peak activity at a Kav of 0.25 and on SDS-PAGE the purified preparations showed peak antigenic activity corresponding to 65,000 daltons. Hydrolysis of the alpha antigens with HCl induced minor changes in the SDS-PAGE patterns and reduction in antigenic activity. Both of the alpha antigens were immunogenic in rabbits. Antisera to the alpha 335 and beta A909 antigens were used to evaluate indirect FAT, CA, RIE, and CIE, in the detection of the antigens in 20 group B isolates. The results indicated that as a single test for the detection of alpha and beta antigens in group B streptococci, FAT or RIE should be preferred.