Genotypic diversity and genotype–phenotype concordance of antimicrobial resistance in methicillin-resistant staphylococci from dogs and cats

Methicillin-resistant staphylococci (MRS) are a cause of major opportunistic infection in dogs and cats and are resistant to several antimicrobial drugs used in veterinary hospitals. In Thailand, data on the genetic background of MRS and its association with clinical features remain limited. Whole genome sequencing (WGS) offers a comprehensive approach for characterizing genetic traits, including antimicrobial resistance genes, and is increasingly considered a valuable tool in clinical laboratories. However, the concordance between phenotypic and genotypic antimicrobial resistance requires further investigation. This study aimed to investigate the genotypic diversity of MRS, its associations with clinical characteristics, and the concordance between genotypic and phenotypic antimicrobial resistance. The 47 clinical MRS isolates included in this study comprised S. pseudintermedius (61.7%), S. aureus and S. coagulans (14.9% each), S. ureilyticus (4.3%), and S. haemolyticus and S. warneri (2.1% each). Polyclonal methicillin-resistant S. pseudintermedius (MRSP) strains were found across various infections, predominantly harboring SCCmec V(5C2&5). MRSP ST1386, ST496, and seven novel sequence types were reported for the first time in Thailand. Certain sequence types of MRSP ST1386 and ST433 were isolated from multiple infection sites. Although virulence gene profiles varied, their frequency did not correlate with clinical improvement. The overall genotype-phenotype concordance was 93.19%, with highest agreement for penicillin and erythromycin (100%) and fluoroquinolones and clindamycin (97.87%). Discordance was mostly due to genotypic resistance but phenotypic susceptibility. MRSP polyclonal shift was observed. WGS is a powerful tool for monitoring MRS genotypic diversity and resistance in veterinary medicine and shows promise for phenotype prediction with improved species-specific resistance databases.