Phenotyping and Genotyping of Antibiotic-Resistant Escherichia coli Isolated from a Natural River Basin

• Published in: Environmental science & technology 2008-05, Vol.42 (9), p.3415-3420
• Main Authors: Hu, Jianying, Shi, Jiachen, Chang, Hong, Li, Dong, Yang, Min, Kamagata, Yoichi
• Format: Article
• Language: English
• Subjects: Animals; Anti-Bacterial Agents - pharmacology; Antibiotics; Applied sciences; Bacteriology; beta-Lactams - metabolism; Chickens; China; Drug resistance; Drug Resistance, Bacterial; Drug Resistance, Microbial; E coli; Ecotoxicology and Human Environmental Health; Escherichia coli - genetics; Escherichia coli - metabolism; Exact sciences and technology; Freshwater; Genotype; Genotype & phenotype; Gram-positive bacteria; Humans; Microbial Sensitivity Tests; Phenotype; Pollution; River basins; Rivers; Sulfonamides - analysis; Swine; Tetracycline - analysis
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es7026746

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 sulfonamide, and three β-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. tet(M), a tetracycline-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 tet(M) in E. coli might have been transferred from other bacterial species through horizontal gene transfer, which was supported by the fact that no tet(M) 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.