Antimicrobial Resistance and Virulence Genes of Enterococci Isolated from Water Buffalos Subclinical Mastitis

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This study aimed to investigate the antimicrobial resistance and virulence genes of enterococci isolated from water buffalo’s subclinical mastitis cases. The antimicrobial susceptibilities of the isolates were determined by the disc diffusion method. Identification at the species level of enterococci, virulence [aggregation substance (asa1), gelatinase (gelE), cytolysin (cylA), enterococcal surface protein (esp), and hyaluronidase (hyl)] and resistance genes [macrolide (ermA, ermB, mefA/E) and tetracycline (tetK, tetL, tetM, tetO, and tetS)] were investigated by polymerase chain reaction (PCR). Overall, Enterococcus spp. was recovered from 65 of 200 (32.5%) mastitic milk samples, comprising E. faecium (n=26), E. durans (n=22), E. faecalis (n=12), and E. hirae (n=5). Most isolates (56.9%) were susceptible to all tested antibiotics. The rest of the isolates showed various rate of resistance against rifampicin (23.1%), tetracycline (21.5%), quinupristin-dalfopristin (10.8%), ciprofloxacin (7.7%), erythromycin (6.2%), and chloramphenicol (3.1%). Out of 65 enterococci, only 16 (24.6%) were detected to have virulence genes, of which 12 were positive for gelE, seven were positive for esp, two were positive for asa1, and one was positive for hlyA. The gene cylA was not detected in any isolate tested. Resistance to tetracycline was mainly associated with tetM. Two erythromycin-resistant isolates were positive for ermB, and one was positive for mefA/E. This study was the first to report species distribution, antimicrobial susceptibility, and virulence traits of enterococci isolated from subclinical mastitis of water buffaloes in Çorum Province, Türkiye.