Isolation and Molecular Characterization of Multidrug-Resistant Strains of Escherichia coli and Salmonella from Retail Chicken Meat in Japan

Sixty-nine Escherichia coli and 10 Salmonella isolates, recovered from retail chicken meat in Hiroshima prefecture, Japan, were assayed for antimicrobial susceptibility, the presence of integrons and antimicrobial resistance genes. Twenty-eight out of 69 (40.6%) of E. coli and all 10 Salmonella isolates were exhibited multidrug resistance phenotypes. The most commonly reported resistance phenotypes were against ampicillin, streptomycin, spectinomycin, kanamycin, tetracycline, and trimethoprim/sulfamethoxazole. PCR screening for integrons showed that 8 (11.6%) of the E. coli isolates were positive for the class 1 integrons and 1 isolate (1.4%) was positive for the class 2 integrons. Among the 10 Salmonella isolates, 9 were positive for class 1 integrons and none was positive for class 2 integrons. The identified antibiotic resistance gene cassettes within the class 1 integrons were dfrA1, dfrA7, aadA1, aadB, and catB3, while dfrA1, sat2, and aadA1 were identified within class 2 integron. The beta-lactamase resistance gene bla(TEM-1) was identified in 12 (17.3%) of E. coli isolates and in only one of the Salmonella isolates. The bla(CMY-2) gene, encoding AmpC beta-lactamase, was detected in 16 (23.2%) of the E. coli isolates only. Conjugation experiments demonstrated that there was plasmid-mediated transfer of bla(CMY-2) and bla(TEM-1). These results highlighted the role of retail chicken meat as a potential source for multidrug-resistant strains of E. coli and Salmonella. To the best of our knowledge, this is the 1st report of isolation and molecular characterization of multidrug-resistant strains of E. coli from retail chicken meat in Japan.