This study evaluated the cell invasion ability (CIA) of Streptococcus canis isolates, and clarified the relationship between high-frequency CIA and its microbiological features. Of the companion animal-origin isolates (n = 117) that were obtained in 2017, 40 isolates were randomly selected with the host information, with two human blood-origin isolates included. CIA was measured using human colon carcinoma epithelium and the hemolytic activity (HA) using sheep blood, along with S. canis M-like protein (SCM) allele typing, sequence type (ST) determination, and antimicrobial resistance (AMR) phenotyping/genotyping. CIA measurements revealed that 19 and 24 isolates had high- and low-frequencies, respectively. HA assessment revealed that 24 and 19 isolates were categorized as high- and low- level, respectively. No difference was observed in the high-/low-level HA between the high- /low-frequency CIA populations. A significant difference was found in the high-/low-frequency CIA between the SCM group I/II populations. Additionally, a significantly higher CIA was found in the SCM allele type 10/type 11 than in the others. A significant association was observed between high-frequency CIA and the ST21/ST41 populations. No difference was found in the high-/low-frequency CIA between the presence and absence of the AMR phenotype/genotype. These observations suggest a relationship between high-frequency CIA and its microbiological characteristics (SCM allele type 10/type 11 or ST21/ST41).
Keywords: M-like protein; Streptococcus canis; antimicrobial resistance; cell invasion; sequence type.