title: Molecular profiles of group B streptococcal surface protein antigen genes: relationship to molecular serotypes.
abstract: The study of surface protein antigens of group B streptococci (GBS) is important for understanding of the pathogenesis and epidemiology of infection, and several of these antigens have been proposed as components of GBS conjugate vaccines. In a previous study, we developed a novel PCR-and-sequencing system for identification of GBS serotypes and serosubtypes based on the capsular polysaccharide synthesis (cps) gene cluster. In this study, we used published sequences to develop PCR assays for identification of genes encoding GBS surface proteins including C alpha (bca), C alpha-like proteins 2 and 3 (alp2 and alp3), Rib (rib), and C beta (bac). We showed that the prototype R reference strain, Prague 25/60, contained a novel alpha-like protein antigen gene (the proposed alp4), which presumably encodes an atypical, but antigenically similar, R-like protein. Initial evaluation of these gene-specific assays showed excellent specificity. By combining cps serotypes, serosubtypes, and surface protein gene profiles, we were able to divide 224 GBS isolates into 31 serovariants. GBS bac-positive strains could be further subtyped into 11 groups and 20 subgroups. Our results confirmed and extended reported associations between some cps serotypes and serosubtypes, on the one hand, and surface protein genes, on the other: serosubtypes III-1 and III-2 were associated with rib, serosubtype III-3 with alp2, serotype Ib with bca and bac, and serotype V with alp3. The associations between serotype Ia and bca, bca repetitive unit, and bca repetitive unit-like sequence-containing genes need to be studied further. These PCR-based methods will provide an alternative and objective tool for subtyping of GBS based on surface protein antigen genes.
authors.affiliation: Centre for Infectious Diseases and Microbiology Laboratory Services, Institute of Clinical Pathology and Medical Research, Westmead, New South Wales, Australia.
authors.forename: Fanrong
authors.initials: F
authors.lastname: Kong
authors.forename: Sonia
authors.initials: S
authors.lastname: Gowan
authors.forename: Diana
authors.initials: D
authors.lastname: Martin
authors.forename: Gregory
authors.initials: G
authors.lastname: James
authors.forename: Gwendolyn L
authors.initials: GL
authors.lastname: Gilbert
mesh_terms: D000942:Antigens, Bacterial; D000954:Antigens, Surface / Q000235:genetics*; D001426:Bacterial Proteins / Q000235:genetics*; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics; D016133:Polymerase Chain Reaction / Q000379:methods*; D012680:Sensitivity and Specificity; D012703:Serotyping; D013292:Streptococcus agalactiae / Q000145:classification* / Q000235:genetics
chemical_list: D000942:Antigens, Bacterial; D000954:Antigens, Surface; D001426:Bacterial Proteins; D008565:Membrane Proteins; C081277:Rib protein, Streptococcus agalactiae; C077961:alpha C protein, group B streptococci