Dissemination of ESBL-producing E. coli ST131 through wastewater and environmental water in Switzerland.

The E. coli lineage ST131 is a major cause of multidrug-resistant urinary tract and bloodstream infections worldwide. Recently emerged ST131 sublineages spread globally within few years, but their dissemination routes are incompletely understood. In this study, we investigate the potential role of wastewater and surface water in the spread of extended-spectrum β-lactamase (ESBL)-producing ST131. Streams, lakes, and two wastewater treatment plants (WWTPs) in the canton of Zug, Switzerland, were consecutively sampled over 1.5 years. ST131 was detected in 38% of the samples taken downstream (1-5 km) of WWTP discharge sites, but usually absent in water bodies distant from urban areas or WWTP discharge. Specific strains were repeatedly isolated (≤5 pairwise cgSNP distance) from wastewater or river sites downstream of effluent discharge, indicating their repeated entry or persistence in WWTPs in large concentrations. Genetic characterization of the ESBL-producing water isolates revealed a predominance of clades A and C1 and an emerging ciprofloxacin-resistant sublineage with mutations in quinolone resistance determining regions (QRDR) within clade A. Multiple isolates belonged to internationally circulating sublineages, including C1-M27 and papGII + sublineages with chromosomally encoded ESBLs. This study demonstrates that the clinically relevant E. coli lineage ST131 pollutes river ecosystems, representing a significant challenge to public health and to technologies to minimize their entry into the water environment.