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Genotyping of the capsule gene cluster (cps) in nontypeable group B streptococci reveals two major cps 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.

SUBMITTER: Sellin M

PROVIDER: S-EPMC87398 | biostudies-literature | 2000 Sep

REPOSITORIES: biostudies-literature

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Genotyping of the capsule gene cluster (cps) in nontypeable group B streptococci reveals two major cps allelic variants of serotypes III and VII.

Sellin M M Olofsson C C Håkansson S S Norgren M M

Journal of clinical microbiology 20000901 9

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) analy ...[more]

PMID: 10970395

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Project description:Although virulence of Streptococcus pneumoniae is associated with its capsule, some pathogenic S. pneumoniae isolates lack capsules and are serologically nontypeable (NT). We obtained 64 isolates that were identified as NT "pneumococci" (i.e., bacteria satisfying the conventional definition but without the multilocus sequence typing [MLST]-based definition of S. pneumoniae) by the traditional criteria. All 64 were optochin sensitive and had lytA, and 63 had ply. Twelve isolates had cpsA, suggesting the presence of a conventional but defective capsular polysaccharide synthesis (cps) locus. The 52 cpsA-negative isolates could be divided into three null capsule clades (NCC) based on aliC (aliB-like ORF1), aliD (aliB-like ORF2), and our newly discovered gene, pspK, in their cps loci. pspK encodes a protein with a long alpha-helical region containing an LPxTG motif and a YPT motif known to bind human pIgR. There were nine isolates in NCC1 (pspK(+) but negative for aliC and aliD), 32 isolates in NCC2 (aliC(+) aliD(+) but negative for pspK), and 11 in NCC3 (aliD(+) but negative for aliC and pspK). Among 52 cpsA-negative isolates, 41 were identified as S. pneumoniae by MLST analysis. All NCC1 and most NCC2 isolates were S. pneumoniae, whereas all nine NCC3 and two NCC2 isolates were not S. pneumoniae. Several NCC1 and NCC2 isolates from multiple individuals had identical MLST and cps regions, showing that unencapsulated S. pneumoniae can be infectious among humans. Furthermore, NCC1 and NCC2 S. pneumoniae isolates could colonize mice as well as encapsulated S. pneumoniae, although S. pneumoniae with an artificially disrupted cps locus did not. Moreover, an NCC1 isolate with pspK deletion did not colonize mice, suggesting that pspK is critical for colonization. Thus, PspK may provide pneumococci a means of surviving in the nasopharynx without capsule. IMPORTANCE The presence of a capsule is critical for many pathogenic bacteria, including pneumococci. Reflecting the pathogenic importance of the pneumococcal capsule, pneumococcal vaccines are designed to elicit anticapsule antibodies. Additional evidence for the pathogenic importance of the pneumococcal capsule is the fact that in pneumococci all the genes necessary for capsule production are together in one genetic locus, which is called the cps locus. However, there are occasional pathogenic pneumococci without capsules, and how they survive in the host without the capsule is unknown. Here, we show that in these acapsular pneumococci, the cps loci have been replaced with various novel genes and they can colonize mouse nasopharynges as well as capsulated pneumococci. Since the genes that replace the cps loci are likely to be important in host survival, they may show new and/or alternative capsule-independent survival mechanisms used by pneumococci.

Dataset Information

Genotyping of the capsule gene cluster (cps) in nontypeable group B streptococci reveals two major cps allelic variants of serotypes III and VII.

Publications

Genotyping of the capsule gene cluster (cps) in nontypeable group B streptococci reveals two major cps allelic variants of serotypes III and VII.

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