Genetic analysis of the cps gene clusters in Streptococcus suis and development of a novel genetic typing method that contributes to serotyping

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Streptococcus suis is an important bacterium which can cause severe disease in pigs and humans. S. suis strains are classified into more than 30 serotypes on the basis of the antigenicity of their capsular polysaccharides (CPs). In this study, we analyzed the complete set of S. suis cps gene clusters. Our data implied the possibility of the transfer of the entire or partial cps gene clusters among S. suis strains, as well as the influence of spontaneous mutations in a single or a few genes on the antigenicity of some serotypes. Accumulation of these gene transfers and small-scale mutations may have generated the antigenic diversity of S. suis CPs. In addition, by targeting the genes conserved in several serotypes and the serotype-specific genes identified in our analysis, we have developed multiplex PCR-based cps-typing method composed of 2 steps that contributes to the serotyping of S. suis.