Leung, MHY; (2012) Phenotypic and genotypic diversity of Streptococcus pneumoniae strains in Tanzania and the United Kingdom. Doctoral thesis , UCL (University College London).

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Abstract

Streptococcus pneumoniae is a prevalent etiological agent of diseases and a common colonizer. During pneumococcal colonization, adaptation and evolution of the organism is thought to occur by horizontal gene transfer. Heterogeneity in distribution of genes between strains contributes to the global supragenome pool greater than the genome of any single strain. Co-colonization of multiple strains, therefore, enables an organism to expand its supragenome and hence its adaptive potential. In this study, the development and design of a single primer-pair PCR- and sequence-based serotyping (sequetyping) method for surveillance of prevalent serotypes is presented. Serotypes including those covered in the latest conjugate vaccines were identified at least to the serogroup level. This method thus shows promise in its application in routine determination of prevalent serotypes. The sequetyping method was applied to perform a systematic analysis of characterizing pneumococci isolated from healthy Tanzanian children in an attempt to determine phenotypic and genotypic diversities (multilocus sequence typing) within colonization events. Through this work evidence is presented to support that previous studies analyzing serotype diversity alone is an underestimate of true strain diversity during co-colonization events. Determination of competence peptide allelic variants revealed significant differences in proportions of pherotypes in two geographical locations. The majority of co-colonization events showed multiple pherotypes, indicating that co-colonization events may provide an optimal condition for genetic exchanges. Intra-serotype variations in the capsular gene cpsB were observed and the difference of this variation between serotypes. Nucleotide differences were mapped to specific domains of the CpsB protein, which may affect the enzymatic activity of this regulatory protein. Sequencing comC from presumptive strains of S. pseudopneumoniae revealed that comC6.1 is a common pherotype of this organism. It is proposed that this gene may be a potential target for differentiation between S. pseudopneumoniae from S. pneumoniae and other streptococcal species.

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