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: bla(Tem), StrA, aadA, sul1, sul2, gyrA, 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, bla(Tem) genes were observed for 62% of E. coli isolates and 20% of 65 Salmonella Kentucky. The StrA 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 gyrA 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.