Population biology of Streptococcus pneumoniae isolated from oropharyngeal carriage and invasive disease The GenBank accession numbers for the sequences of the trpA/B alleles determined in this study are AF157817 to AF157826.

Abstract

The population structure of Streptococcus pneumoniae in a sample of 134 carried antibiotic-susceptible isolates, and 53 resistant and susceptible invasive isolates, was examined using a DNA-based version of multilocus enzyme electrophoresis: multilocus restriction typing (MLRT). This involved RFLP analysis of PCR products generated from nine loci of housekeeping genes located around the pneumococcal chromosome. The combination of alleles at each of the nine loci gave an allelic profile or restriction type (RT). All carried (throat or nasopharyngeal) isolates from children or adults in Oxford and Manchester, UK, and from an HIV-seropositive cohort in Nairobi, Kenya, showed an epidemic population structure. Twelve carried clonal groups, each with different serotypes, were identified at both locations within the UK. Almost all of the carried clones examined (16/17) were found to possess identical RTs or sequence types (STs) to invasive isolates, indicating that frequently carried clones are also associated with cases of invasive disease. As expected from previous studies, the population of 53 invasive, mainly penicillin-resistant, isolates was also found to be at linkage equilibrium. Serotype switching was identified among 14% of RTs that possessed two or more members, or 5.7% of individual isolates within these RTs. In support of a population structure in which there is frequent recombination, there is also clear evidence that the trpA/B locus within pneumococci has evolved by horizontal gene transfer. A non-serotypable isolate from an HIV-seropositive patient in Kenya was clearly genetically distinct from other strains studied, with unique alleles at eight out of nine loci examined. However, it was initially identified as a pneumococcus by a 16S RNA gene probe (Gen-Probe), optochin susceptibility and the presence of pneumolysin and autolysin.

Spontaneous sequence duplications within capsule genes cap8E and tts control phase variation in Streptococcus pneumoniae serotypes 8 and 37

“…It has been shown that trpB/A genes exhibit substantial allelic variation (Muller-Graf et al, 1999). These genes were sequenced from wild-type organisms and their capsule phase-variable derivatives to show that these mutants had arisen from the organisms used to inoculate sorbarod filters and were not contaminants.…”

“…Recently, it has been reported that the presence of pneumococcal capsule is also important for murine carriage (Magee & Yother, 2001). Although the majority of pneumococci from clinical isolates are capsulate, a previous population genetic study of pneumococcal carriage identified two pneumococcal isolates from pernasal swabs of children and one from a pernasal swab of a female human immunodeficiency virus-positive patient that were non-serotypable (Muller-Graf et al, 1999). In addition, acapsulate pneumococci have been associated with outbreaks of conjunctivitis (Ertugrul et al, 1997).…”

“…A proportion of these acapsular colonies (3?3 %, serotype 8 strain; 1?9 %, serotype 37 strain) were found to be capsule phase variable as they could revert to capsular phenotype (phase-ON). Phase-OFF and phase-ON phenotypes were confirmed using the Quellung reaction.It has been shown that trpB/A genes exhibit substantial allelic variation (Muller-Graf et al, 1999). These genes were sequenced from wild-type organisms and their capsule phase-variable derivatives to show that these mutants had arisen from the organisms used to inoculate sorbarod filters and were not contaminants.…”

Genetic Basis for the New Pneumococcal Serotype, 6C

“…Perhaps the wciN 6C gene is from an organism other than pneumococci and was inserted into the 6A capsule gene locus. Horizontal gene transfers between S. pneumoniae and another bacterial species have been demonstrated with antibiotic resistance genes (5,18) and have been suggested to occur for capsule gene loci because they have low GϩC content (2). The "flanking regions" are known to be critical for homologous recombination in pneumococci (21).…”

Pilot Study of the Genetic Diversity of the Pneumococcal Nasopharyngeal Flora among Children Attending Day Care Centers

“…Although some studies have described the serotype diversity among carriage pneumococcal isolates in cultures (8,11,12), to our knowledge, only two recent studies have addressed their genetic diversity (16,28). We further characterized the strains isolated from heterogeneous samples for genetic determinants involved with DNA transfer and for susceptibility to lysis by antimicrobial agents.…”