Evidence of vancomycin-resistant Staphylococcus aureus, multidrug-resistant S. aureus, and Enterococcus faecium-causing mastitis in Thailand and Cambodia

Background and Aim: Bovine mastitis, an inflammatory condition of the mammary gland, is a critical economic issue in the dairy industry. Antimicrobial resistance (AMR) to mastitis-causing pathogens poses a significant threat to dairy operations in Thailand and Cambodia. This study investigates the AMR of mastitis pathogens in Thailand and Cambodia. It focuses on detecting methicillin-resistant Staphylococcus aureus, vancomycin-resistant S. aureus (VRSA), and vancomycin-resistant enterococci by identifying the presence of mecA, vanA, and van8 genes in bacterial isolates. Materials and Methods: A total of 65 bacterial isolates (55 S. aureus from Thailand and 10 Enterococcus faecium from Thailand and Cambodia) were analyzed. Disk diffusion tests were conducted for antibiotic susceptibility, and polymerase chain reaction was employed to detect AMR genes. Results: S. aureus isolates showed resistance to penicillin (21.8%), tetracycline (9.1%), and gentamycin (7.3%). Three isolates were identified as multidrug-resistant (MDR), resistant to tetracycline, gentamycin, and penicillin. E. faecium isolates exhibited high resistance to tetracycline (100%) and penicillin (90%), with 60% classified as MDR. Phenotypic analysis identified VRSA in 11% of S. aureus isolates. However, mecA, vanA, and van8 genes were not detected in any isolate. Conclusion: Mastitis pathogens in this study pose significant AMR challenges, especially with MDRS. aureus and E. faecium, and phenotypically VRSA without the vanA gene. The findings highlight the need for judicious antibiotic use in dairy farms and further studies with broader sampling.