Isolation and characterization of group B streptococcal type antigens X and R.

The group B streptococcal surface antigens X and R were isolated from culture supernatant by ammonium sulphate precipitation and subsequent high performance gel filtration (HPLC). The type antigens appeared in numerous protein bands. Type antigen X was in the range of 180 kD, type antigen R, in the range of 116 kD. The protein antigens reacted specifically with their homologous antisera in Western blot analysis and in immunoelectrophoresis, indicating that there was no immunological relationship between both proteins. Preparative isoelectric focusing of the X and R antigens revealed for both proteins isoelectric points at acid pH. Specific antibodies produced against the purified proteins could be used for routine serotyping without further absorption.