Background: In recent decades, bacterial antibiotic resistance (especially in enterococci) has become a significant problem
for human and veterinary medicine. One of the most important antibiotic resistances in enterococci, vancomycin resistance, is
encoded by van gene family.
Objectives: The aim of this study was to investigate antibiotic resistance to vancomycin in enterococci and thegenes responsible
for this resistance.
Materials and Methods: Two-hundred and thirty enterococcal isolates from pigs (207 isolates), chickens (15 isolates) and humans
(eight isolates) were phenotypically and genotypically tested for resistance to vancomycin by minimum inhibitory concentration
(MIC) and polymerase chain reaction (PCR). The van genes were confirmed by gene sequencing.
Results: Of the total isolates, 19% were phenotypically resistant to vancomycin, while nearly 15% contained either vanC1 or vanC2
gene. One resistant E. casseliflavus isolate with pig origin (MIC > 8 μg/mL) contained both vanC1 and vanC2 genes. Furthermore,
one vanC1 was found in a sensitive E. faecalis isolate of pig origin (MIC ≤ 4 μg/mL) and one vanC2 in a resistant E. faecium isolate
of chicken origin (MIC > 32 μg/mL). These genes were not accompanied by other van genes. Other detected genes were vanA in 11 E.
faecium isolates of chicken origin (MIC > 32 μg/mL). No vanB genes were found. Gene sequencing results showed 100% identity with
GenBank reference genes.
Conclusions: The current report is the first report on the detection of vanC1 and vanC2 genes in one enterococcal species with
pig origin. This report is important as it proves the horizontal transfer of various vanC genes to one species possibly due to the
compatibility class of plasmids. Furthermore, detection of vanC genes in E. faecalis and E. faecium isolates is important as it suggests
that resistance to vancomycin in non-motile enterococci can be encoded by several mechanisms.