Insight into the specific virulence related genes and toxin-antitoxin virulent pathogenicity islands in swine streptococcosis pathogen Streptococcus equi ssp. zooepidemicus strain ATCC35246.

BACKGROUND: Streptococcus equi ssp. zooepidemicus (S. zooepidemicus) is an important pathogen causing swine streptococcosis in China. Pathogenicity islands (PAIs) of S. zooepidemicus have been transferred among bacteria through horizontal gene transfer (HGT) and play important roles in the adaptation and increased virulence of S. zooepidemicus. The present study used comparative genomics to examine the different pathogenicities of S. zooepidemicus.

RESULTS: Genome of S. zooepidemicus ATCC35246 (Sz35246) comprises 2,167,264-bp of a single circular chromosome, with a GC content of 41.65%. Comparative genome analysis of Sz35246, S. zooepidemicus MGCS10565 (Sz10565), Streptococcus equi. ssp. equi. 4047 (Se4047) and S. zooepidemicus H70 (Sz70) identified 320 Sz35246-specific genes, clustered into three toxin-antitoxin (TA) systems PAIs and one restriction modification system (RM system) PAI. These four acquired PAIs encode proteins that may contribute to the overall pathogenic capacity and fitness of this bacterium to adapt to different hosts. Analysis of the in vivo and in vitro transcriptomes of this bacterium revealed differentially expressed PAI genes and non-PAI genes, suggesting that Sz35246 possess mechanisms for infecting animals and adapting to a wide range of host environments. Analysis of the genome identified potential Sz35246 virulence genes. Genes of the Fim III operon were presumed to be involved in breaking the host-restriction of Sz35246.

CONCLUSION: Genome wide comparisons of Sz35246 with three other strains and transcriptome analysis revealed novel genes related to bacterial virulence and breaking the host-restriction. Four specific PAIs, which were judged to have been transferred into Sz35246 genome through HGT, were identified for the first time. Further analysis of the TA and RM systems in the PAIs will improve our understanding of the pathogenicity of this bacterium and could lead to the development of diagnostics and vaccines.