Genetic Analysis Of The Capsular Polysaccharide Synthesis Locus And Development Of Molecular Serotyping For Streptococcus Suis

Streptococcus suis is an important zoonotic agent causing severe diseases in pigs and humans. To date,33serotypes of S. suis have been identified based on antigenic differences in the capsular polysaccharide. The capsular polysaccharide synthesis (cps) locus encodes proteins/enzymes that are responsible for capsular production and variation in the capsule structures are the basis of S. suis serotyping. Multiplex and/or simplex PCR assays have been developed for15serotypes based on serotype-specific genes in the cps gene cluster. In the first part of this study, we developed a series of multiplex PCR (mPCR) assays to identify the33currently known S. suis serotypes. To identify serotype-specific genes for mPCR, the entire genomes of33serotype reference strains were sequenced using whole genome high-throughput sequencing, and the cps gene clusters from these strains were identified and compared. We developed4sets mPCR assays based on the polysaccharide polymerase gene wzy, one of the serotype-specific genes. The assays can identify all serotypes except for two pairs of serotypes:1and14,2and1/2, which have no serotype-specific genes between them. The first assay (setl) identifies12serotypes (serotypes1to10,1/2, and14) that are the most frequently isolated from diseased pigs and patients; the second (set2) identifies10serotypes (serotypes11to21except14); the third (set3) identifies the remaining11serotypes (serotypes22to31, and33); and the fourth (set4) identifies a new cps cluster of S. suis discovered in this study in isolates that agglutinated with antisera for serotypes29and21. In the second part of this study, we sequenced32untypable strains using both agglutinating by antisera and the mPCR scheme (set1-4) described above, and ten new cps cluster types were discovered and analysed. The new cps cluster were named as cps â… -cps â…©, another2mPCR assays (set5, set6) for identifying them were developed based on the wzy gene, set5identifies7new cps cluster type cps â… -cps â…¦, set6identifies the remaining3new cps cluster type cps â…§-cps â…©. The multiplex PCR assays developed in this study provide a rapid and specific method for molecular serotyping of S. suis.