Antimicrobial resistance in Enterococcus spp. isolated from laying hens of backyard poultry flocks

Introduction and objective. Enterococci belonging to human and animal gastrointestinal flora are widely-distributed in the environment. They are opportunistic bacteria that can cause severe infections, with the ability to acquire, express and transfer antimicrobial resistance. The aim of the present study was to investigate antimicrobial resistance profiles of Enterococcus spp. strains isolated from cloacal swabs of laying hens of small backyard flocks. Materials and methods. Susceptibility to 21 antimicrobial agents was tested by the disc diffusion method in 115 Enterococcus spp. strains. Vancomycin and ampicillin minimum inhibitory concentrations and high-level aminoglycoside resistance tests were also performed. Results. Isolates showed resistance mainly to aminoglycosides, eritromycin, fluoroquinoles, tetracycline and nitrofurantoin. 19 (16.5%) isolates showed a high level of resistance to streptomycin, but no high level resistance to gentamycin. No significant resistance was detected for vancomycin. Several strains (45; 39.1%) showed combined resistance to macrolides, lincosamides and streptogramin B. 61 (53%) isolates were classified as multidrug-resistant (MDR) and 6 (5.2%) strains as possibly extensively drug-resistant (XDR). E. faecium was the most prevalent antimicrobial resistant species, followed by E. faecalis and E. durans. Conclusions. The results show that the risk of dissemination of antimicrobial resistant enterococci is related not only to the birds of large commercial flocks, but also to the birds of small backyard flocks. Thus, laying hens of hobby flocks, which share the outside environment with people, could represent a hazard for public health by providing a conduit for the entrance of resistance genes into the community.