Genomic characteristics and antimicrobial resistance of the underreported zoonotic pathogen Streptococcus pasteurianus and its co-colonization with Streptococcus suis.

Streptococcus pasteurianus is an opportunistic pathogen affecting various animals and is an underreported zoonotic threat. It is also a causative agent of swine streptococcosis and can be co-detected with Streptococcus suis, another significant pig and zoonotic pathogen. However, the dynamics of co-colonization between these pathogens, along with the genomic features and antibiotic resistance profiles of S. pasteurianus, remain poorly understood. In this study, we developed a multiplex PCR (mPCR) assay to detect S. pasteurianus and S. suis in 827 tonsil samples from healthy pigs, with 81 samples positive for both pathogens. Pan-genome analysis revealed an open pan-genome, indicating an adaptable genome. Antibiotic resistance gene analysis identified 21 distinct genes, including the first identification of mef(A), msr(D), optrA, lnu(G), spw, dfrF, and fexA in S. pasteurianus. Strain WUSP082 carried 15 resistance genes, many of which were located on mobile genetic elements. ICE carries tet(O), erm(B), and ant(6)-Ia, showing 99.10 % sequence similarity to S. suis ICE. GI, containing tet(L) and tet(M), shares 99.94 % similarity with S. suis 89-kb pathogenicity island. Plasmid, carrying fexA, optrA, and erm(A), shares 98.85 % sequence homology with Enterococcus faecium plasmid pW6-2. All 15 strains collected from our lab displayed multidrug resistance, being resistant to at least four classes of antibiotics. Mouse infection experiments demonstrated the pathogenic potential of WUSP082, isolated from the tonsil of a healthy pig. This study advances our understanding of the genomic characteristics and antimicrobial resistance of S. pasteurianus, offering valuable insights for the surveillance and management of this under-recognized zoonotic pathogen.