Molecular characterization of extended spectrum beta lactamase producing Escherichia coli in two different wastewater treatment plants in Hatay Province, Türkiye

Wastewaters are considered as hotspot for multidrug resistant bacteria and genes, especially for extended spectrum beta lactamase producing Escherichia coli (ESBL-EC), which pose significant public health concern. Conventional wastewater treatment plants (WWTPs) are not designed to remove such resistant bacteria before discharge. This study, therefore, aimed to evaluate and compare the performance of two municipal WWTPs in eliminating ESBL-EC in Hatay province, Türkiye. The isolates were further characterized by antimicrobial susceptibility testing, pulsed-field gel electrophoresis (PFGE) and resistance gene analysis. A total of 24 wastewater samples [influent (n = 12) and effluent (n = 12)] were collected from both conventional and advanced biological WWTP. A total of 66 ESBL-EC were isolated and confirmed as ESBL producer. The abundance of ESBL-EC was significantly more prevalent in the influent water samples (mean 3.86 ± 0.11 log cfu/ml), when compared to the effluent wastewater samples (mean 2.20 ± 0.27 log cfu/ml). According to the PFGE results (cut-off > 85%), 16 isolates were clonally related, whereas 49 isolates were singletons and one isolate could not be evaluated. Besides beta-lactam antibiotics, the isolates were highly resistant to tetracycline (63.63%) and fluoroquinolones (43.93%). The bla_CTX-M gene was the most frequently detected gene in the isolates (86.36%), among which the bla_CTX-M-15 type (86.36%) was the most frequently detected. At least two disinfectant resistance genes were also detected in each of the isolates. Even though both WWTP were found to be effective in reducing ESBL-EC counts, not well enough to complete elimination, showing the potential public health risk.