Antibiotic susceptibility and molecular characterization of resistance genes among Escherichia coli and among Salmonella subsp. in chicken food chains

Objective: To investigate the occurrence of resistance genes among Escherichia coli(E. coli) and Salmonella subsp. isolated in chicken food chains in Phnom Penh, 2012–2013.Methods: Six hundred eighty two E. coli and 181 Salmonella Albany, Corvallis, and Kentucky strains were examined for susceptibilities to eight antimicrobials and following resistance genes were identified by PCR: blaTem, Str A, aad A, sul1, sul2, gyr A, Tet(A), and Tet(B).Results: E. coli presented high resistances to tetracycline, amoxicillin, and sulfamethoxazole(63.1%–76.1%). Salmonella Albany and Salmonella Kentucky traduced high resistance percentages to amoxicillin, tetracycline, sulfamethoxazole, and nalidixic acid(84.6%–100%). Among amoxicillin-resistant isolates, blaTemgenes were observed for 62% of E. coli isolates and 20% of 65 Salmonella Kentucky. The Str A gene was prevalent in 36% of 331 aminoglycoside-resistant E. coli and 90% of 40 aminoglycoside-resistant Salmonella Corvallis. The sul2 gene was predominant among sulfamethoxazole-resistant isolates, for 56% of 431 E. coli and 53% of 66 Salmonella Corvallis; the sul1 gene was observed in 54% of Salmonella Albany. The Tet(A) resistance gene was prevalent in E.coli(86%), Salmonella Corvallis(82%), Salmonella Kentucky(84%). High percentages of gyr A genes observed among nalidixic-acid resistant E. coli(91%), Salmonella Albany(92%), Salmonella Corvallis(75%) and Salmonella Kentucky(85%).Conclusions: Important occurrences of resistance gene were observed among E. coli and Salmonella in chicken food chains in Cambodia.