Population Genomics, Virulence Traits, and Antimicrobial Resistance of Streptococcus suis Isolated in China

<i>Streptococcus suis</i> is a significant zoonotic pathogen of public health importance. In this study, whole-genome sequencing of 177 isolates of <i>Streptococcus suis</i>, isolated from diseased swine across 15 provinces in China between 2017 and 2019, was performed. A total of 23 serotypes and 28 ST types were identified, with serotypes 2 and 3 comprising 50.8% of the isolates, and sequence types ST353 and ST117 accounting for 23.7%. Clustering analysis based on known virulence-associated factors (VAFs) resulted in the identification of four distinct clusters, and virulence was assessed using animal models, including a unique, highly virulent cluster designated as cluster I. Drug susceptibility testing indicated that 97.7% of the isolates were multidrug-resistant. A total of 26 resistance-associated genes were identified within the genome, 18 of which were associated with integrative and conjugative elements (ICEs) and/or integrative mobilizable elements (IMEs). Nevertheless, our understanding of <i>suis</i> virulence in terms of phylogeny remains incomplete. This study contributes to the understanding of the population structure and genetic characteristics of <i>suis</i>, provides a framework and novel partitioning approach for future investigations into its virulence and pathogenicity, and complements the data on antibiotic resistance.