M-like protein SrM is not crucial to the virulence of a novel isolate of Streptococcus equi subsp. ruminatorum from Macaca mulatta.

In this study, a Streptococcus strainnamed FJ1804, was isolated from a blood sample collected from a dead Macaca mulatta in China and, was subsequently classified as Streptococcus equi subsp. ruminatorum (S.e. ruminatorum) through 16S rRNA gene sequence analysis. After whole genome sequencing and analysis, an M-like protein encoding gene that encodes an SrM protein that is homologous to the crucial S.e. zooepidemicus crucial virulence factor SzP, was identified in the genome of FJ1804. To determinethe function of SrM in this bacterium, a strain deleted of srm as well as a complement strain were constructed. The results of in vitro cell adherence, invasion and phagocytosis assays and in vivo animal challenge and histopathology showed that the anti-phagocytosis was decreased and the adherence rate was increased in the srm deletion strain, whereas the invasion rate, pathological features and LD values inboth zebrafish and BALB/c mice model showed no difference compared to that observed for the WT strain. To the best of our knowledge, this is first of an infection caused by S.e. ruminatorum, which is a newly identified zoonotic pathogen, in Macaca mulatta, and our data suggest that, compared with other S.e. zooepidemicus strains, the SzP homologous protein is not crucial to the virulence of this bacterium.