Phenotyping and genotyping of antihiotic-resistant Escherichia coli isolated from a natural river basin

摘要

Scientists have become increasingly concerned about the occurrence of antibacterial resistance in the environment. In this study, Escherichia coli resistant to one or more antibiotics among nine antibiotics was screened from Wenyu River Basin in Beijing, China, with mean frequency of 48.7 +/- 8.7 of 388 isolates in summer and 47 +/- 6 of 236 isolates in winter. The mean multiantibiotic resistance (MAR) index in summer was 0.11 +/- 0.03, slightly lower than that (0.14 +/- 0.04) in winter. Most frequent resistance appeared for sulfonamides, tetracycline, and ampicillin. The distribution of 20 tetracycline, three sulfonamicle, and three beta-lactam resistance genes was assessed in the resistant isolates. While 97 of the ampicillin (AMP) resistant mechanism could be explained by the resistance gene TEM, 90 of the tetracycline (TC) and 96 of the sulfonamide (SXT) resistances could be explained by tet(A), tet(B), tet(M), and their combinations and sul(I), sul(II), sul(III), and their combinations, respectively. team), a tetra cycline-resistant gene originally detected in Gram-positive bacteria, and its combinations with tet(A) or tet(B) were first detected in E. coli isolated from a natural river basin, suggesting that team) in E coli might have been transferred from other bacterial species through horizontal gene transfer which was supported by the fact that no team) was detected in the isolates of human and chicken sources, except for only one isolate from swine. The source of sulfonamide-resistant E coli in the river was supposed to be mainly from humans, based on a comparison of the sulfonamide resistance genotypes in animals and humans.