Structural and Genetic Diversity of Group BStreptococcusCapsular Polysaccharides

Abstract

Group B Streptococcus (GBS) is an important pathogen of neonates, pregnant women, and immunocompromised individuals. GBS isolates associated with human infection produce one of nine antigenically distinct capsular polysaccharides which are thought to play a key role in virulence. A comparison of GBS polysaccharide structures of all nine known GBS serotypes together with the predicted amino acid sequences of the proteins that direct their synthesis suggests that the evolution of serotype-specific capsular polysaccharides has proceeded through en bloc replacement of individual glycosyltransferase genes with DNA sequences that encode enzymes with new linkage specificities. We found striking heterogeneity in amino acid sequences of synthetic enzymes with very similar functions, an observation that supports horizontal gene transfer rather than stepwise mutagenesis as a mechanism for capsule variation. Eight of the nine serotypes appear to be closely related both structurally and genetically, whereas serotype VIII is more distantly related. This similarity in polysaccharide structure strongly suggests that the evolutionary pressure toward antigenic variation exerted by acquired immunity is counterbalanced by a survival advantage conferred by conserved structural motifs of the GBS polysaccharides.

Lectin Microarray Reveals Binding Profiles of Lactobacillus casei Strains in a Comprehensive Analysis of Bacterial Cell Wall Polysaccharides

“…However, the kind of PS structure important for their activity and how these molecules exert their activities on host cells are still open questions. In addition, it has been shown that extracellular PSs of Streptococcus thermophilus (39) and group B Streptococcus capsular PSs are highly diverse (6). It is well-known that pathogenic bacteria, such as hemolytic streptococci, often change their outer surface glycan profile to escape the host immune defense mechanism (5).…”

Sequence type 1 group B Streptococcus , an emerging cause of invasive disease in adults, evolves by small genetic changes

“…The relatively low rate of recombination among ST-1 strains allowed for elucidation of discrete GBS loci under positive selection, only some of which have been previously identified as important for GBS host-pathogen interaction (22,26,35). Thus, in conjunction with our Alp findings, these data provide a new platform for investigating why ST-1 GBS strains have emerged as a major cause of invasive disease in nonpregnant adults, such as analysis of the previously unstudied TCS encoded by rdf_0314-0315.…”

Simultaneous detection and serotype identification of Streptococcus agalactiae using multiplex PCR and reverse line blot hybridization

“…To compare with previously published primer pairs for serotype II-, VII-and VIII-specific PCRs (Borchardt et al, 2004;Cieslewicz et al, 2005) we used cpsIIK, cpsVIIM and cpsVIIIJ, respectively, rather than cpsH as the targets for primers and probes (Kong et al, 2002). We also designed one GBS-specific primer pair and two GBSspecific probes (Ke & Bergeron, 2001).…”

“…Nine GBS capsular polysaccharide serotypes and corresponding capsular polysaccharide synthesis (cps) gene clusters are recognized (Cieslewicz et al, 2005). Their distribution varies according to geographic location and study population (Schuchat, 1998).…”