Genomic characteristics of multidrug-resistant Streptococcus pluranimalium isolated from a cow with mastitis in Xinjiang, China.

Streptococcus pluranimalium has emerged as a significant zoonotic pathogen, associated with bovine mastitis and a range of infections in multiple animal species and humans. In this study, a multidrug-resistant S. pluranimalium strain, designated XJSP, was isolated from milk samples collected during a clinical mastitis outbreak on a dairy farm in Xinjiang, China. Whole-genome sequencing revealed its genome comprised 2066,720 bp with a GC content of 38.78 %, harboring 1933 coding sequences, 44 tRNAs, 5 rRNA operons, 5 genomic islands, 3 prophage regions, and a 5007 bp plasmid pXJSP-1 carrying four resistance genes: LRA-7, salB, ermK, and lnuA. Phylogenetic analysis positioned S. pluranimalium within a distinct clade alongside S. ictaluri, S. cuniculipharyngis, S. hillyeri, and S. entericus. Pan-genome analysis of 25 global S. pluranimalium strains identified 880 core genes and extensive accessory gene content, reflecting high genetic diversity. The XJSP strain exhibited resistance to ceftriaxone, cefotaxime, erythromycin, ofloxacin, chloramphenicol, and tetracycline, and carried 66 antimicrobial resistance genes and 212 virulence factor genes. Comparative plasmid analysis indicated potential horizontal transfer of resistance genes among Streptococci. These findings enhance our understanding of the genomic architecture, antimicrobial resistance mechanisms, and evolutionary relationships of S. pluranimalium, highlighting its potential risk for interspecies transmission and its implications for public health.