Genotyping of the Capsule Gene Cluster (cps) in Nontypeable Group B Streptococci Reveals Two Majorcps Allelic Variants of Serotypes III and VII

Abstract

Forty group B Streptococcus (GBS) isolates obtained from Europe and the United States previously reported to be nontypeable (NT) by capsule serotype determination were subjected to buoyant density gradient centrifugation. From nearly half of the isolates capsule-expressing variants could be selected. For characterization of the remaining NT-GBS isolates, the capsule operon (cps) was amplified by the long-fragment PCR technique and compared by restriction fragment length polymorphism (RFLP) analysis. The patterns from serotype reference isolates (n ‫؍‬ 32) were first determined and used as a comparison matrix for the NT-GBS isolates. Using two restriction enzymes, SduI and AvaII, cluster analysis revealed a high degree of similarity within serotypes but less than 88% similarity between serotypes. However, serotypes III and VII were each split in two distant RFLP clusters, which were designated III 1 and III 2 and VII 1 and VII 2 , respectively. Among the isolates that remained NT after repeated Percoll gradient selections, two insertional mutants were revealed. Both were found in blood isolates and harbored insertion sequence (IS) elements within cpsD: one harbored IS1548, and the other harbored IS861. All other NT-GBS isolates could, by cluster analysis, be referred to different serotypes by comparison to the RFLP reference matrix. In pulsed-field gel electrophoresis of SmaI-restricted chromosomal DNA, patterns from allelic type 1 and 2 isolates were essentially distributed in separate clusters in serotypes III and VII. A covariation with insertion sequence IS1548 in the hylB gene was suggested for serotype III, since allelic type III 1 harboring IS1548 in hylB, clustered separately. The variation in serotype VII was not dependent on the presence of IS1548, which was not detected at any position in the type VII chromosome.

Genomic Analysis Reveals the Molecular Basis for Capsule Loss in the Group B Streptococcus Population

“…The first step in the investigation of the molecular basis for the loss of capsule expression in Streptococcus agalactiae was the selection of a wide panel of strains devoid of capsule. GBS serotyping by Lancefield immuno-precipitation or by latex agglutination can indeed provide discrepant results regarding the NT phenotype [ 28 , 29 ]. To investigate capsule expression by a more accurate flow-cytometry based approach, we generated monoclonal antibodies against purified CRM-conjugated polysaccharides of the five most frequent capsular genotypes, i .…”

Emergence of a Streptococcus dysgalactiae subspecies equisimilis stG62647-lineage associated with severe clinical manifestations

“…demonstrated that the insertion of IS1548 immediately upstream of the laminin binding gene lmb , was associated with an ~5-fold increase both in the transcription of lmb , and in the phenotypic bacterial adhesion to laminin 38 . Conversely, insertion of IS1548 into the hylB and cpsD genes, abrogated the production of hyaluronidase and bacterial capsule, respectively 37 , 39 . Of note, IS1548 has also been documented in the covRS -system in S. pyogenes .…”

Identification of novel cps locus polymorphisms in nontypable group B Streptococcus

“…Most NT isolates express surface proteins: alpha and beta components of the C protein or one or more of the R protein antigens, Rib, and Alp1-4 proteins (Benson et al, 2002;Kong et al, 2002b). These isolates can be genotyped and distinguished by PFGE and by the expressed surface-protein antigens Sellin et al, 2000). The C proteins were recognized by Lancefield as protective determinants found in GBS of serotypes Ia and Ib (reviewed by Lindahl et al, 2005).…”