Qnr Prevalence in <i>Escherichia coli</i> Isolates from Wastewater from Livestock Farms in Hamedan, Iran

Abstract

Background: Multidrug-resistant (MDR) Escherichia coli represent a serious public health risk, leading to higher rates of illness, death, and economic costs. The presence of antibiotics in livestock wastewater contributes to the development of resistance among commensal and environmental bacteria, which can diminish the effectiveness of these drugs in treating both humans and animals. Objectives: This research aimed to examine the patterns of antibiotic resistance and the prevalence of qnrS resistance genes. Methods: This cross-sectional study was conducted on 24 active dairy cattle farms in Hamedan, Iran, selected based on the presence of an accessible wastewater discharge point releasing into residential or agricultural areas. A total of 96 wastewater samples were collected from June to December 2023. Inclusion criteria for samples were a minimum volume of 1 liter, collection within the study period, and processing within 24 hours under refrigerated conditions. Eosin methylene blue agar was utilized to isolate E. coli from wastewater samples. The Kirby-Bauer diffusion susceptibility method was employed to assess the antimicrobial susceptibility and resistance patterns of the isolated E. coli strains. DNA amplification was conducted in polymerase chain reaction (PCR) on a thermos-cycler, for 35 cycles, using a master mix and specific primers for the qnrS gene. Results: Over 60% of 40 strains isolated from 96 wastewater samples were found to be resistant against nalidixic acid (NA), ceftazidime, trimethoprim-sulfamethoxazole (SXT), and piperacillin (PRL). The qnrS resistance gene was identified in 15% of the E. coli. Conclusions: The findings of this study reveal that the wastewater in Hamedan is tainted with antibiotic-resistant E. coli, which poses a significant risk to agricultural communities located downstream. This contamination not only threatens public health by fostering antibiotic resistance among microbial populations but also underscores the need for improved wastewater treatment to lower bacterial levels to safe standards before it is utilized in aquaculture and agriculture.