Genotypic and Phenotypic Features of Eye-Origin Streptococcus canis Isolates from Dogs in 2021: Relatedness with Clonal Complex 46 and Antimicrobial Resistance.

The eye (including the cornea) and ear canal are the major sources of Streptococcus canis in companion animal practice. In this study, we aimed to clarify the genotypic and phenotypic features of eye-origin isolates collected in 2021 compared to ear-origin isolates collected in 2021 and eye-origin isolates collected in 2017. Of the 102 isolates in 2021, 9 eye-origin isolates were enrolled. Twenty ear-origin isolates in 2021 and 13 eye-origin isolates in 2017 were included as controls. Genotypic analyses included profiling of virulence-associated genes (VAGs; inl, sagA, slo, scp, lbp, fbp, gbp, ap1, fp1, and brp), S. canis M-like protein (SCM) allele typing, multilocus sequence typing, and antimicrobial resistance (AMR) genotyping and phenotyping analyses including hemolytic activity (HA) measurement and AMR phenotyping. One 2017-eye-origin isolate displayed high-level HA; the others displayed low-level HA. No association was evident between the 2021-eye-origin population and the detection rate of each VAG. There was no association between the 2021-eye-origin population and the main SCM allele 2. A significant association was evident between the 2021-eye-origin population and the main clonal complex (CC) 46 containing sequence type (ST) 46/ST2. A significant association was also detected between the 2021-eye-origin population and AMR phenotypes/genotypes. Our observations suggest unique microbiological features (CC46 with AMR phenotypes/genotypes) among the 2021-eye-origin population.