Abstract

Background: Considering the importance of hospital wastewaters as potential reservoirs for the dissemination of bacterial pathogens such as Escherichia coli and antibiotic resistance genes in the environment, the need for such information becomes imperative. Methods: E. coli strains were isolated from hospital wastewater sources in Tehran, Iran, over a 24-month sampling period (Jun 2014-Jun 2016) and identified using standard bacteriological methods. Quinolone resistance among the strains was determined using Kirby-Bauer method and the frequency of plasmid-mediated quinolone resistance genes (qnrA, qnrB, qnrS) was investigated by PCR. Results: In total, 80 E. coli strains were isolated during the study period, of which 51 (63.8) isolates were resistant to tested antibiotics. Of note, 13 isolates were resistant to all the antibiotics employed. The highest rates of antibiotic resistance were obtained for nalidixic acid (60), followed by norfloxacin (30), and ciprofloxacin (25). Of the 51 quinolone-resistant strains, 24 (47.1) isolates harbored qnr genes. None of the isolates harboured the qnrA gene, while 11 (45.8) and 7 (29.2) isolates contained qnrB and qnrS, respectively. Conclusion: Our findings showed high rates of quinolone resistance (63.8) and qnr genes, underlining the importance of hospital wastewaters as reservoirs for dissemination of potentially pathogenic E. coli and horizontal gene transfer between other waterborne bacterial species. Other possible mechanisms of resistance should also be investigated for better characterization of quinolone-resistant E. coli isolates.