Persistence of Antibiotic-Resistant Escherichia coli Following Chlorine Disinfection of Hospital Wastewater

Background and Aim: This study investigated the prevalence of antibiotic-resistant Escherichia coli in untreated and treated wastewater from a hospital wastewater treatment system and assessed their persistence after chlorine disinfection. Materials and Methods: The study included three main steps. First, E. coli was isolated from untreated and treated wastewater samples. Second, antibiotic susceptibility was assessed phenotypically. Ten antibiotics were tested using the Kirby–Bauer disk diffusion method, while colistin susceptibility was evaluated by broth microdilution to determine the minimum inhibitory concentration (MIC). Colistin results were interpreted according to the EUCAST breakpoint for Enterobacterales, with MIC ≤۲ mg/L considered susceptible and MIC >۲ mg/L considered resistant. Third, selected resistance genes related to ESBL production, colistin resistance, and carbapenem resistance were detected by PCR after thermal DNA extraction. Results: Escherichia coli was detected in ۵ of ۱۰ untreated wastewater samples (۵۰.۰%) and ۶ of ۱۰ treated wastewater samples (۶۰.۰%), with no statistically significant difference (p > ۰.۰۵). Because the sample size was small and more than one isolate was obtained from some samples, the results should be interpreted as detection-frequency data rather than evidence of bacterial-load reduction. Ampicillin resistance was the most common phenotype in untreated wastewater isolates (۸۶.۷%) and was detected in all treated wastewater isolates (۱۰۰%). Fosfomycin resistance was the least common phenotype in treated wastewater isolates (۵.۶%). The genes blaTEM, blaCTX-M-۱ group, blaCTX-M-۹ group, and mcr-۱ were detected in isolates from both wastewater types, while selected carbapenemase genes were detected in treated-wastewater isolates. Conclusion: The treatment system reduced conventional physicochemical pollutants but did not fully remove detectable antibiotic-resistant E. coli or selected resistance genes.

کلیدواژه ها:

Escherichia coli ، Antibiotic Resistance Genes ، Hospital Wastewater ، Chlorination ، Antimicrobial Resistance