Characterization of antibiotic resistance genes and bacteria in a municipal water resource recovery facility.

Municipal water resource recovery facilities (WRRFs) are important sources of antibiotic-resistant bacteria and genes (ARB and ARGs). In this study, antibiotic-resistant total heterotrophic bacteria (THB ) counts (CFU/ml) cultivated from influent, effluent of activated sludge process, and outflow of disinfection unit of an urban WRRF were investigated for the presence of 16, 32, 64, and 128 μg/ml of nine antibiotics. The isolates of Pseudomonas spp., Acinetobacter spp., and Escherichia coli obtained from effluent of activated sludge process were subjected for molecular identification by detecting the 16S rRNA gene sequences. Additionally, using the polymerase chain reaction method (PCR), the isolates were investigated for the presence of bla , bla , bla , bla , sul1, and qnrS genes. According to the results, the abundance of THB counts was not significantly reduced by the biological treatment except for cefixime and sulfamethoxazole; it also increased for some antibiotics after disinfection unit. The average removal efficiency of THB resistant to ciprofloxacin, sulfamethoxazole, and ceftazidime were 7.9 ± 1.7%, 41.8 ± 2.1%, and 14.4 ± 6.2%, respectively. Also, all the tested isolates were resistant to at least four antibiotics. For all antibiotics, the resistance ratio (THB /THB) significantly increased in the effluent and after chlorination unit. Among 12 resistant isolates, bla and sul1 genes were the most frequently detected ones involved in 92% and 83% of the isolates, respectively. Both bla and sul1 genes were found in 100% of E. coli, and 83% and 67% of Pseudomonas spp. isolates, respectively. Further efforts are necessary to limit the transmission of ARB and ARGs from WRRFs into the environment and prevent human health threats. PRACTITIONER POINTS: The ratio of resistance significantly increased after biological treatment. Up to 40% of heterotrophic bacteria in the effluent was antibiotic resistant. bla and sul1 genes were more prevalent (92%) in all isolates of bacteria. Both bla and sul1 genes were found in 100% of E. coli isolates. Pseudomonas spp. holds bla and sul1 genes in 83% and 67% of isolates, respectively.