Serotype 14 Variants of the France 9V ⁻³ Clone from Baltimore, Maryland, Can Be Differentiated by the cpsB Gene

Abstract

European serotype 14 variants of the France 9V؊3 clone, which have arisen through recombination events involving the penicillin binding protein 1a (pbp1a) gene, have cpsB sequences distinct from those of the 9V ؊3 clone. Serotype 14 variants of the 9V؊3 clone have not been compared to genetically diverse serotype 14 strains isolated from an entire metropolitan area in the United States. All serotype 14 non-penicillin-susceptible Streptococcus pneumoniae strains causing invasive disease in Baltimore, Md., from 1995 to 1996 were compared by using pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), pbp1a PCR restriction profiles, and cpsB and pbp1a sequences. The cpsB genes from strains of 13 serotypes also were analyzed to assess the correlation with serotype. Twenty-seven percent (3 of 11) of the serotype 14 strains were related by PFGE and MLST to the 9V ؊3 clone. The serotype 14 variants from Baltimore, unlike the European variants, were related neither to the 9V ؊3 clone nor to the R6 strain from positions 1498 to 1710 of the pbp1a gene. All serotype 14 strains had cpsB sequences that differed by <1% (0 to 5 of 476 bp) from each other and that were >16% (78 to 83 of 476 bp) divergent from that of the 9V ؊3 clone. Allowing for a 2-bp difference in the cpsB sequence resulted in the highest correlation between the cpsB gene and serotype. Overall, 95% (84 of 88) of the strains were classified correctly by serotype with the cpsB sequence. The distal recombination site of the Baltimore serotype 14 variants of the 9V ؊3 clone was not identical to that of the European serotype 14 variants. The cpsB gene was serotype specific regardless of whether capsular switching occurred. Although the correlation between serotype and the cpsB sequence was high, the overall diversity of the cpsB gene within a serotype likely will limit the role of this gene in a sequence-based serotyping method.Pneumococci are naturally transformable, with recombination rates 10-fold higher than mutation rates (5). Griffith et al. (8a) first described pneumococcal transformation in 1928, while Avery et al. determined that the transforming factor was DNA (1). Strains which are found to be highly related by pulsed-field gel electrophoresis (PFGE) and multilocus sequencing typing (MLST) may have different serotypes, indicating serotype capsular recombination (2,3,18,24). The capsular locus is comprised of a series of alphabetically named capsular genes, which are flanked by the conserved genes dexB and aliA; approximately 5.8 kb downstream from aliA is the penicillin binding protein 1a (pbp1a) gene (2). Since a capsular locus has been identified for a variety of serotypes, the capsular genes are attractive targets for a sequence-based serotyping method. An association between some capsular gene sequences and serotype has been noted in the literature, even for strains which have undergone capsular transformation (2, 3).The France 9V Ϫ3 pneumococcal clone is 1 of approximately 20 international clones and has been detected as serot...

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Sequetyping: Serotyping Streptococcus pneumoniae by a Single PCR Sequencing Strategy

“…The region is located at the 5= end of the cps locus, a region previously known to be relatively conserved (7,31,44,46,48). It is notable that this region is present in the pneumococcus only, as no amplification is obtained with S. mitis, S. oralis, and S. pseudopneumoniae organisms, which have traditionally been difficult to differentiate (4,32).…”