Localization of surface immunogenic protein on group B streptococcus

The localization and accessibility of the group B streptococcus (GBS) surfa ce immunogenic protein (Sip) at the surface of intact GBS cells were studie d by flow cytometric assay and immunogold electron microscopy. Antibodies p resent in pooled sera collected from mice after immunization with purified recombinant Sip efficiently recognized native Sip at the surfaces of the di fferent GBS strains tested, which included representatives of all nine sero types. Examination of GBS cells by immunogold electron microscopy revealed that the Sip-specific antibodies attached preferentially to polar sites and the septal region. This result confirmed that Sip is exposed at the intact -cell surface, but it also suggests that its distribution is restricted to certain regions of the cell.