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.

Phenotypic and Genotypic Characterization of Group B Streptococcal Isolates in Southern Brazil

“…Molecular serotyping methods would probably increase their typeability. However, a decreased capacity for capsular polysaccharide synthesis, noncapsulated phase variation, or cps gene cluster modification could prevent proper serotype identification (8,27). Our study confirms the high level of beta-lactam susceptibility of GBS (6,40).…”

“…Previous studies reported occurrence rates of NT strains ranging from 1 to 18% (3,21,27,50). Our numbers (7.1%) included colonizing, noninvasive, and invasive isolates.…”

Multiplex PCR Assay for Direct Identification of Group B Streptococcal Alpha-Protein-Like Protein Genes

“…Relationships between serotypes and surface protein genes were noted but to a lesser degree than previously reported (10,12). The association of serotypes Ia, Ib, and II with the alpha protein, of serotype III with Rib, and of serotypes V and VIII with Alp3 was found, but these associations were not absolute.…”

“…In two cases (reference strain Prague 10/84 and a bovine strain), no surface protein gene was detected. The absence of a surface protein gene in GBS isolates, although rare, has previously been reported (10).…”

The prevention of neonatal group B streptococcal disease: a report by a working group of the Medical Screening Society

“…4,49,52,53 The antibody response was observed to persist for over a year in the mother and the passive protection in the neonate persisted for at least three months, hence it would be expected to protect against late-onset disease. 4,48,50,54 Moreover, the IgG antibody is bactericidal. 4 At present, a fully effective vaccine should be pentavalent, so as to induce antibodies against all five GBS serotypes that cause disease (see section on Microbiological procedures in detecting GBS colonization), but a univalent GBS vaccine active against a single surface protein shared by the five serotypes is under development.…”