High Prevalence Of Human-Associatedescherichia Coliin Wetlands Located In Eastern France

Escherichia colithat are present in the rivers are mostly brought by human and animal feces. Contamination occurs mostly through wastewater treatment plant (WWTP) outflows and field amendment with sewage sludge or manure. However, the survival of these isolates in river-associated wetlands remains unknown. Here, we assessedE. colipopulation structure in low-anthropized wetlands located along three floodplains to identify the major source of contamination of wetlands, whose functioning is different from the rivers. We retrieved 179E. coliin water samples collected monthly from 19 sites located in eastern France over 1 year. Phylogroups B1 and B2 were dominant in theE. colipopulation, while phylogroup A was dominant in isolates resistant to third-generation cephalosporins, which harbored the extended-spectrum beta-lactamase (ESBL) encoding genesbla(CTX-M-15)andbla(CTX-M-27)in half of the cases. The high proportion of isolates from human source can be attributed to WWTP outflows and the spread of sewage sludge. We analyzed the distribution of the isolates belonging to the most human-associated phylogroups (B2 and D) on a phylogenetic tree of the whole species and compared it with that of isolates retrieved from patients and from WWTP outflows. The distribution of the threeE. colipopulations was similar, suggesting the absence of a specific population in the environment. Our results suggest that a high proportion ofE. coliisolates that reach and survive in low-anthropized environments such as wetlands are from human source. To the best of our knowledge, this is the first study assessingE. colicontamination and resistance genes in natural freshwater wetlands.