Prevalence and diversity of M-like protein (SCM) gene in Streptococcus canis isolates from diseased companion animals in Japan: Implication of SCM allele

Streptococcus canis (Sc)-origin M-like protein (SCM) binds to plasminogen and immunoglobulin G and facilitates anti-phagocytic properties. We aimed to determine the prevalence and diversity of the scm gene in Sc isolates from diseased companion animals in Japan and to propose potential SCM alleles of amino acid (AA) sequences. We collected beta-hemolytic streptococci from diseased animals with host information nationwide in 2015 and 2017. After Sc identification and scm gene amplification and sequencing, the gene's prevalence and relationship between its presence and host information were determined. Furthermore, phylogenetic trees of AA sequences were constructed, and classification and distribution of SCM alleles based on variations of AA sequences were conducted. The scm detection rates were 70.6% (n = 48, 2015) and 82.9% (n = 97, 2017). There was a relationship between scm presence and Tokyo in 2015 and 2017. We found an association between scm detection and dogs in 2017 alone. Major sequence sizes were 1311 bp, 1308 bp, and 1305 bp. Using the phylogenetic trees of AA sequences, we confirmed shared positions of five identical sequence patterns in both periods. Nine SCM alleles were determined with six signal-peptide types. Most prevalent alleles were type 1, type 2, and type 4 in both periods. Our observations suggest prevalence and diversity of scm in animal-origin Sc isolates in Japan.