Phenotypic and genotypic antibiotic resistance profiles of Escherichia coli O157 from cattle and slaughterhouse wastewater isolates

The aims of this study were to determine the minimal inhibition concentration of 20 different antibiotics on cattle and slaughterhouse wastewater Escherichia coli O157, including both Shiga toxigenic E. coli O157 (STEC O157) and non-Shiga toxigenic strains (non-STEC O157) by the Epsilometer test, and to determine the antibiotic resistance gene profiles of the isolates by PCR. A total of 102 cattle and slaughterhouse wastewater E. coli O157 isolates including 96 E. coli O157:H7(+) (81 non-sorbitol fermenting [NSF] STEC O157:H7, 12 NSF non-STEC O157:H7, and three sorbitol fermenting [SF] non-STEC O157:H7) and six non-STEC O157:H7(-) isolated from 744 cattle and slaughterhouse wastewater samples collected within a 2-year period were assessed. Of 93 NSF E. coli O157:H7 isolates, 19 were resistant to tetracycline and sulfamethoxazole, 14 to trimethoprim, 13 to cefoxitin, 11 to streptomycin, 10 to ampicillin, eight to chloramphenicol, six to cephalothin, four to cefaclor, four to aztreonam, and four to nalidixic acid. In six of the E. coli O157:H7(-) isolates, tetracycline resistance was detected while five of them were also resistant to ampicillin, sulfamethoxazole, and trimethoprim. In PCR analysis, 26.0 % (25/96) of the NSF E. coli O157:H7(+) and all of the E. coli O157:H7(-) isolates harbored one or more antibiotic resistance genes. While tetA, tetB, tetC, strA, strB, and sulI genes were detected from a number of the isolates, tetD, tetE, tetG, cmlA, floR, sulII, aadA, and ampC genes were not detected in any of the isolates. Results suggest a high antibiotic resistance in E. coli O157:H7(+)/H7(-) cattle and wastewater isolates. The majority of our resistant isolates, antibacterial resistance genes did not correlate with observed phenotypic resistance. Other resistance traits and regulatory factors that mediate antibiotic resistance should be included in further antimicrobial resistance investigations.