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

Abstract

One hundred and twenty-three Salmonella enterica isolated in Italy from chicken meat and carcasses and from quail carcasses were analyzed to determine their levels of antibiotic resistance using antibiograms (phenotypic method) and PCR amplification of antimicrobial resistance-associated genes (genotypic method). The isolates were screened for the ability to grow in the presence of antibiotics (ampicillin, gentamicin, sulfamethoxazole and tetracycline) and for the presence of the following genes: pse-1, ant (3")-Ia, qacEΔI and sul-1, tetA, tetB and tetG. The most frequently isolated serotypes in 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 11.1% of the isolates. Of the isolates from quail carcasses, 89.2% exhibited resistance to sulfamethoxazole, and 24.3% displayed phenotypic multi-drug resistance to ampicillin, gentamicin, sulfamethoxazole and tetracycline; a complete genotypic profile (pse-1, ant (3")-Ia, qacEΔI and sul-1, tetA, tetB and tetG) was obtained for 27.0% of the isolates. Among 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 a multi-drug resistance to ampicillin, sulfamethoxazole and tetracycline; only one isolate, S. Enteritidis, contained 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%).