Contamination of aquatic environments by antibiotics and antibiotic-resistant faecal bacteria is a great concern at the worldwide scale. Discharges of WWTP and runoff or leaching of soils are the main pathways for inputs of these contaminants in surface water. In order to better understand the fate of antibiotics and faecal bacteria populations (Escherichia coli, Enterococcus), these contaminants have been studied along two continuums: (i) medical center - WWTP - river and (ii) cattle farm - urban area. A multi-residue chemical methodology (LC/MS/MS) was developed to detect low concentrations (ng.L-1) of 34 antibiotics in water along the two continuums. Together with these chemical analyses, the structures of faecal bacteria were characterized by antibiotic resistance, distribution of phylogroups A, B1, B2, D, occurrence of integrons, virulence factors for E. coli; and diversity of species, antibiotic resistance and associated resistant genes for Enterococcus. The study of the two continuums has shown that compounds found in rivers were not the most prescribed (penicillins), but the more enduring molecules (quinolones, sulfonamides, macrolides). However, antibiotic concentrations (1ng.L-1 to 100ng.L-1) are insufficient to exert a selective pressure on antibiotic-resistant bacteria. Land use, vicinity of contamination sources and farm practices have an impact on (i) levels of contamination by antibiotics and antibiotic-resistant faecal bacteria, (ii) the structure of E. coli and Enterococcus populations in water. Strains of E. coli and Enterococcus from hospital origin have disappeared along the continuum in favor of other well-adapted strains. First assays of modeling using the hydrological model GR have shown the significance of E. coli fluxes during recurrent runoff periods (winter) on a watershed submitted to a main human pressure.
