Prevalence, Molecular Characterisation and Antimicrobial Resistance of Enterococcus faecalis and Enterococcus faecium Isolated from Bovine Mastitis in Poland.

Enterococci are among the most frequently isolated environmental bacteria that cause mastitis in cows. This study aimed to determine the prevalence of virulence genes, as well as phenotypic and genotypic antibiotic resistance, among eighty enterococcal isolates from cases of bovine mastitis in Polish herds. The presence of virulence and antibiotic resistance genes was determined by PCR. E. faecalis isolates were found to carry more virulence genes than E. faecium isolates, including the efaAfs (100%), ace (98.1%), gelE (86.5%), asa1 (63.5%), esp (57.7%) and cylA (17.3%) genes. The efaAfm gene was the only virulence gene detected in E. faecium isolates. This study revealed that E. faecalis showed a higher virulence gene burden. The ermB gene was present in 90.9% of the Enterococcus spp. that were phenotypically resistant to erythromycin. Almost all tetracycline-resistant Enterococcus isolates carried the tet(M) gene (94.3%), either alone or in combination with the tet(L) and tet(O) genes. Three isolates harboured vanC genes and were susceptible to vancomycin (MIC = 4 μg/mL). The results confirm the high level of antimicrobial resistance of enterococci isolated from cows with mastitis and indicate the genes that may be responsible for this resistance.