Detection and characterization of oxazolidinone resistance genes in enterococci from companion animals

Abstract This study characterized drug resistance and virulence in Enterococcus faecalis and Enterococcus faecium isolated from pet dogs and cats in Guangdong Province (Guangzhou, Shenzhen, Dongguan, and Foshan) and Shanghai, China. It investigated potential cross-host transmission and genetic diversity associated with enterococci carrying oxazolidinone resistance genes. Bacterial isolation, antimicrobial susceptibility and virulence phenotype testing, detection of resistance and virulence genes, and whole-genome sequencing were performed. Enterococci isolated from pets exhibited resistance to linezolid and tedizolid, harboring the cfr (D), optrA , and poxtA resistance genes. A strain of E. faecium harbored a plasmid carrying both the cfr (D) and optrA genes. Compared to E. faecalis , E. faecium exhibited a higher hemolysis rate but a lower biofilm formation rate. Thirteen virulence genes were detected in E. faecalis ; detection rates for gelE , sprE , agg , and fsr series genes decreased annually, while rates for the hemolysin cyl series, asa1 , and efaA genes increased. Genomic analysis revealed clonal transmission of optrA - and poxtA -positive E. faecium within pets. Genetic environment analysis implicated IS 1216 as a key facilitator in the dissemination of oxazolidinone resistance genes. These findings demonstrated that pet dogs and cats harbored enterococci carrying oxazolidinone resistance genes, with these strains exhibiting clonal transmission among companion animals.