Distribution of antibiotic resistance genes in enterococcus spp. isolated from mastitis bovine milk

Abstract

In this study, determination of enterococcus species that were isolated from mastitic milk samples, investigation of their susceptibilities to antibiotics and identifi cation of the existence of resistance genes in resistant strains were conducted. The specimens consist of 600 mastitic milk samples that were collected from 242 cows. Isolation of enterococcus was carried out in selective media and 94 (15.6%) Enterococcus spp. were isolated. A total of 94 species of Enterococci were identifi ed using both sequencing and polymerase chain reaction (PCR). Enterococcus spp. isolates belong to 5 different species (E. faecalis, E. faecium, E. durans, E. hirae, E. mundtii) in sequence analysis and 4 different species (E. faecalis, E. faecium, E. durans, E. hirae) were identify by PCR method with specifi c primers. Analyzing 94 enterococcus strains by antibiotic sensitiveness test a high rate of resistance to tetracycline in 77 (81.9%) isolates was shown. The tet resistance genes were identifi ed as follows: 54 were tetM positive, 23 were tetK positive and 17 were positive on tetM and tetK. Resistance to erythromycin was established in 27 (28.7%) isolates (25 ermB) while the chloramphenicol resistance gene was found in 10 (10.7%) of isolates and the cat gene was identifi ed in nine samples and one isolate was resistant to vancomycin (1.06%) with the VanA gene confi rmed. In conclusion, it was shown that E. faecalis has the biggest role in enterococcus originated mastitis and these strains were found to be mostly resistant to tetracycline. One vancomycine resistant isolate that had the VanA gene was also determined.