Vancomycin resistance occurs frequently in Enterococcus species, but has not yet been reported in Streptococcus suis, a previously neglected, newly emergent zoonotic pathogen. In this study, we tested the vancomycin susceptibility of 256 human and swine S. suis isolates from 2005 to 2016 and analyzed the mechanism of vancomycin resistance. We found that one isolate BSB6 was resistant to vancomycin with the MIC value of 4 mg/L and to another eleven kinds of tested antimicrobial agents. Whole genome sequencing showed that chromosomal gene mutations, and acquired genes in ICESsuBSB6 accounted for the resistance phenotypes. ICESsuBSB6 was ∼83-kb in size and encoded two resistance gene regions, ARGR1 and ARGR2. ARGR1 harbored six resistance genes, namely erm(B), aadE-apt-sat4-aphA3 cluster and tet(O/W/32/O), and showed highes similarity with corresponding sequences of S. suis ICESsu32457 and Enterococcus faecalis plasmid pEF418. ARGR2 encoded a vanG-type resistance operon. The resistance region showed highest similarity to that of E. faecalis BM4518 vanG1, but the regulatory region was more similar to that of S. agalactiae GBS-NM vanG2. Vancomycin resistance in isolate BSB6 was inducible. The study is the first report of vanG-type resistance in zoonotic pathogen S. suis and highlights importance of its surveillance.
Keywords: ICEs; Streptococcus suis; Vancomycin resistance; vanG-tpye locus.
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