Developing a cps-genotyping scheme for the emerging zoonotic pathogen Streptococcus parasuis through genetic analysis...

Streptococcus parasuis is an emerging zoonotic pathogen responsible for pneumonia, meningitis, peritonitis, pleuritis, nephritis, cellulitis, cholecystitis, sepsis, and arthritis in humans. The continuous increase in reported human cases of S. parasuis infection indicates its growing threat to public health and highlights the urgent need to monitor its epidemiology. The lack of high-throughput typing tools has seriously impeded the epidemiological surveillance of S. parasuis. Serotyping based on antigenic differences in capsular polysaccharides (CPSs) synthesized by cps loci is widely applied in epidemiological research and routine surveillance of various pathogens. In this study, the genetic characteristics of cps loci extracted from 259 S. parasuis genomes isolated from multiple sources were investigated.

Among the 259 S. parasuis genomes, 142 genomes contained an intact cps locus, while the cps loci of 117 genomes were incomplete due to the limited length of the contigs. The intact cps loci were predominantly located between the flanking genes SSU1210 and SSU1209. The presence of wzy genes in all cps loci suggests that CPSs are synthesized via the Wzx/Wzy pathway in S. parasuis population. Based on sequence alignment of the wzy genes, 109 putative serotypes were identified, 10 of which were associated with human infection. The products of the 2047 cps genes from these 109 putative serotypes were grouped into 870 homology groups, of which 79.66% (693/870) were serotype-specific, indicating substantial genetic diversity within the cps loci. Intraspecies and interspecies exchanges of gene fragments and entire cps loci were observed, contributing to the diversity of CPSs in S. parasuis. A cps-genotyping scheme was developed by using whole-genome sequences to align against a curated database of serotype-specific wzy genes.

The study revealed the genetic characteristics of CPSs in S. parasuis population and developed an easy-to-use, expandable, high-throughput cps-genotyping scheme. This study contributed to the evolutionary research, virulence assessment, and epidemiological surveillance of S. parasuis.