Phenotypic and genotypic features of antibiotic resistance in Salmonella enterica isolated from chicken meat, chicken and quail carcasses

One hundred and twenty-three Salmonella enterica isolated from chicken meat and carcasses and from quail carcasses in Italy were analysed to determine their antibiotic resistance using antibiograms (phenotypic method) and PCR amplification of antimicrobial resistance associated genes (genotypic method). The isolates were screened for ability to grow in presence of antibiotics (ampicillin, gentamicin, sulfamethoxazole and tetracycline) and for presence of the following genes pse-1, ant (3’’)-Ia, qacEI and sul-1, tetA, tetB and tetG. The most frequently isolated serotypes within the sample set were S. Virchow (24.4%), S. Enteritidis (17.1%) and S. Typhimurium (15.4%). Of the isolates from chicken carcasses, 86.1% were resistant to tetracycline, while 30.5% of the identified isolates exhibited phenotypic multi-drug resistance to ampicillin, sulfamethoxazole and tetracycline; the multi-resistance pattern ant (3’’)-Ia/sul-1/tetA+tetB was detected in the 11.1% of the isolates. Of the isolates from quail carcasses, 89.2% exhibited resistance towards sulfamethoxazole and 24.3% displayed phenotypic multi-drug resistance to ampicillin, gentamicin, sulfamethoxazole and tetracycline, and a complete genotypic profile (pse-1, ant (3’’)-Ia, qacEI and sul-1, tetA, tetB and tetG) was obtained for 27.0% of the isolates. Amongst these isolates, S. Typhimurium exhibited the genotypes pse-1/ant(3’’)-Ia/sul-1/tetG and pse-1/ant(3’’)-Ia/sul-1/tetA+tetG. Of the isolates from chicken meat, 60.0% were resistant to tetracycline and 36.0% exhibited multi-drug resistance to ampicillin, sulfamethoxazole and tetracycline; only one S. Enteritidis isolate exhibited the complete genotypic pattern pse-1/ant(3’’)-Ia/sul-1/tetG. The majority of the isolates displaying multi-drug resistance to the three antibiotics were isolated from chicken meat (40.0%).