High occurrence and persistence of antibiotic-resistant enterococci in poultry food samples in Portugal

Objectives: We determined the presence of antibiotic-resistant enterococci (ARE) in commercialized poultry samples from Portugal and analysed their clonal diversity and the resistance genes harboured by these strains. Methods: Ninety-nine retail poultry samples of 10 widely commercialized brands were studied (1999-2001). Samples were enriched and plated on selective media with and without vancomycin, gentamicin, streptomycin or kanamycin. Antibiotic susceptibility was established following standard criteria. Identification and detection of genes coding for resistance were determined by PCR. Clonal relatedness was established by PFGE. Results: A high percentage of samples contained vancomycin-resistant enterococci (VRE) (48%), or enterococci highly resistant (HLR) to gentamicin (34%), streptomycin (32%) or kanamycin (30%). Co-resistance to tetracycline, erythromycin, ciprofloxacin and quinupristin/dalfopristin was observed in most of these isolates. VRE were classified as VanA phenotype-vanA genotype (38% of samples), VanB phenotype-vanA (13%) or VanC phenotype-vanC1 (23%). All HLR to gentamicin isolates contained aac(6')-Ie-aph(2 double prime)-Ia. We detected erm(B) in both erythromycin-resistant and -susceptible isolates. Some VRE and HLR to gentamicin strains were recovered from different samples and brands. Long-term persistence of particular VRE strains (> 2 years), exhibiting different Van phenotypes, was observed. Conclusions: High occurrence of ARE suggests maintenance of selective pressure by the use of antibiotics/other substances in the Portuguese poultry environment. Persistence of a number of widespread PFGE types containing different resistance genes might reflect environmental/host-adapted enterococcal strains that might contribute to the maintenance of antibiotic resistance, thus constituting a resistance reservoir that is non-sensitive to banning interventions.