Streptococcus canis genomic epidemiology reveals the potential for zoonotic transfer.

Streptococcus canis, a multi-host pathogen commonly isolated from dogs and cats, has been occasionally reported in severe cases of human infection. To address the gap in knowledge on its virulence and host tropism, we investigated S. canis genomic epidemiology and report the results of this analysis for the first time. We analysed 59 S. canis whole genome sequences originating from a variety of host species, comprising 39 newly sequenced isolates from UK sources, along with all (n=20) publicly available genomes. Antimicrobial resistance (AMR) phenotype was determined for all 39 available isolates. Genomes were screened for determinants of resistance and virulence. We created a core SNP phylogeny and compared strain clustering to multi-locus sequence typing (MLST) and S. canis M-like protein (SCM) typing. We investigated the dataset for signals of host adaptation using phylogenetic analysis, accessory genome clustering and pan-genome-wide association study analysis. A total of 23 % (9/39) of isolates exhibited phenotypic resistance to lincosamides, macrolides and/or tetracyclines. This was complemented by the identification of AMR-encoding genes in all genomes: tetracycline (tetO 14 %, 8/59; and tetM 7 %, 4/59) and lincosamide/macrolide (ermB, 7 %, 4/59). AMR was more common in human (36 %, 4/11) compared to companion animal (18 %, 5/28) isolates. We identified 19 virulence gene homologues, 14 of which were present in all strains analysed. In an S. canis strain isolated from a dog with otitis externa we identified a homologue of S. pyogenes superantigen SMEZ. The MLST and SCM typing schemes were found to be incapable of accurately representing core SNP-based genomic diversity of the S. canis population. No evidence of host adaptation was detected, suggesting the potential for inter-species transmission, including zoonotic transfer.