Characterization of vancomycin-resistant enterococci isolated from fecal samples of ostriches by molecular methods

The aim of this study was to estimate the occurrence of vancomycin-resistant enterococci (VRE) in fecal samples of ostriches from a farm of Southern Portugal, the mechanisms implicated, and the associated virulence factors, 13 years after the banning of the glycopeptide avoparcin as animal growth promoter in the European Union. Fifty-four fecal samples of ostriches were inoculated in Slanetz-Bartley supplemented with vancomycin (4 microg/mL) for VRE recovery. Susceptibility to 11 antibiotics was performed by disk-diffusion agar method in recovered VRE isolates. The mechanism of resistance to vancomycin and to other antibiotics and the presence of the esp and hyl virulence genes were determined by polymerase chain reaction and sequencing. VRE were detected in 7 of the 54 ostrich fecal samples (13%); Enterococcus durans isolates with the vanA genotype were found in 4 of the 54 fecal samples (7.4%), and Enterococcus gallinarum with the intrinsic vanC1 genotype in the remaining three VRE-positive samples. All vanA-containing E. durans isolates showed resistance to tetracycline and erythromycin, and one of them also to ciprofloxacin; they harbored the erm(B) and tet(M) genes, as well as the specific sequences of Tn916 and Tn5397 transposons, but not the esp or hyl virulence genes. Two of the three vanC1 isolates showed resistance to tetracycline [with the tet(M) gene] and one to erythromycin [with the erm(B) gene], and all three contained the hyl gene. Fecal samples of ostriches represent a reservoir of vanA-containing enterococci that could be transmitted to humans through the food chain.