Characterization of antibiotic resistance genes and virulence factors in faecal enterococci of wild animals in Portugal

Antibiotic susceptibility was tested in 140 non-selected enterococci (73 Enterococcus faecalis, 45 E. faecium and 22 of other species) recovered from faecal samples of 77 wild animals in Portugal. Susceptibility testing for 11 antibiotics (vancomycin, teicoplanin, ampicillin, streptomycin, gentamicin, kanamycin, chloramphenicol, tetracycline, erythromycin, quinupristin-dalfopristin and ciprofloxacin) was determined by disk diffusion and agar dilution methods. Forty-four isolates (31.4%) showed susceptibility to all the antibiotics tested (5.5% of E. faecalis; 62.2% of E. faecium; and 78.6% of E. hirae). Neither ampicillin-resistance nor acquired-vancomycin-resistance was detected and 1.4% of the isolates showed high-level-resistance for gentamicin or streptomycin. Tetracycline and erythromycin resistances were shown in 28.6% and 20.1% of the isolates, respectively. Antibiotic resistance genes were studied by polymerase chain reaction (PCR) and sequencing and tet(M) + tet(L), erm(B) or aac(6')-aph(2") genes were detected in most of tetracycline-, erythromycin- or gentamicin-resistant enterococci respectively. Genes encoding virulence factors were studied by PCR and a wide variety of virulence genes were detected in most of E. faecalis isolates but were rarely found in E. faecium and not detected in the other species. The prevalence of genes encoding virulence factors in E. faecalis was as follows: cpd (98.6%), ge/E (75.3%), agg (30.1%), fsr (17.8%), ace (9.6%) and esp (4.1%). Low percentages of antibiotic resistance was found in the faecal enterococci of wild animals but a wide variety of virulence genes were detected among E. faecalis isolates although were rare in the other species.