Abstract:Objective To perform biological characterization and genomic analysis for a multidrug-resistant Streptococcus strain isolated from the tonsils of a dead piglet, thus elucidating its phenotypic and genotypic characteristics.Methods The tonsillar tissue homogenate from the dead piglet was inoculated into the Streptococcus enrichment medium for enrichment culture. The enriched culture was then streaked onto Columbia blood agar medium for Streptococcus isolation. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), a biochemical identification system, and 16S rRNA gene sequencing were employed for strain identification. The minimum inhibitory concentrations (MICs) were determined by the broth microdilution method. Whole-genome sequencing was conducted via the Illumina platform. The ResFinder database was used to analyze the resistance genes, and mutations in the genes encoding penicillin-binding proteins (PBPs) were investigated through multiple sequence alignment.Results The phylogenetic analysis based on 16S rRNA gene sequences identified the isolate as Streptococcus orisratti. Antimicrobial susceptibility testing revealed that the strain was resistant to penicillin G, erythromycin, clindamycin, and compound sulfamethoxazole, and it exhibited reduced susceptibility to linezolid. Whole-genome analysis identified the presence of the macrolide and lincoamide resistance gene ermB and the oxazolidinone resistance gene optrA. Furthermore, multiple mutations were detected in the genes encoding PBPs.Conclusion This study reports the first isolate of S. orisratti harboring both ermB and optrA and exhibiting resistance to penicillin. It highlights the capacity of porcine-derived streptococcal strains to acquire multidrug resistance genes, underscoring the need for increased vigilance regarding the resistance traits and transmission risks of animal-derived streptococci.
