Detection of vancomycin resistance genes with polymerase chain reaction in enterococci isolated from mastitis infection in cows

Abstract

This study aimed to determine the prevalence of enterococci and the presence of vancomycin resistance genes in the context of mastitis infections, which cause economic losses and reduced yield in dairy cows in the Balıkesir province. This is the most comprehensive study conducted in Turkey and Europe on vancomycin resistance in enterococci, both conventionally and genetically. A total of 108 mastitic cow milk samples were collected and sent to laboratory for microbiologic examination by veterinarians from 52 different private dairy farms in Balıkesir city which had 10 or more Holstein and/or Simmental cows, between November 2020 and June 2021. From the milk samples, 28 Enterococcus spp. isolates were identified. Vancomycin resistance was found in 13 of these isolates (46.4%) through disc diffusion and Vancomycin E-tests. The PCR method revealed the presence of the following resistance genes: vanA in 11 isolates, vanB in 4 isolates, vanC1 in 1 isolate, vanC2 in 10 isolates, and vanC3 in 5 isolates. In 4 isolates, the vanA, vanB, vanC2, and vanC3 genes were detected together. Additionally, 1 isolate contained vanA, vanB, and vanC1 genes. Since vanA and vanB resistance genes can be transferred via transposons or plasmids, the presence of vanA and vanB positive Enterococcus spp. strains in this study suggests a potential risk for the spread of resistance genes, and poses a threat to public health. This study found a high prevalence of vancomycin resistance in enterococci isolated from mastitic milk, especially in terms of vanA and vanB genes positivity. There is a concern that milk intended for human consumption could become contaminated with Enterococcus spp., posing potential risks for human infections. Therefore, routine monitoring of VRE in milk is considered important for public health.