Fate of Antibiotics and Antibiotic-Resistant Fecal Bacteria in Water and Sediments from the Contamination Source to the Estuary: Impact and/or Resilience? Resilience to Contamination by Antibiotics

The aim of this study based on a multidisciplinary research program (FLASH) (FLASH (FLuxes of Antibiotic and Antibiotic-resistant bacteria and the corresponding genes in Surface Hydrosystems) a research project founded by CNRS EC2CO/GIP Seine-Aval), associating chemists, hydrologists, and clinical and environmental microbiologists, was to monitor the impact of antibiotic prescription in human and veterinary practices on water and sediment contamination by antibiotic and Escherichia coli (antibiotic resistance, integrons) and Enterococci (diversity, antibiotic resistance, and the corresponding genes) along a medical center–WWTP–river continuum. For this purpose, a multi-residue chemical methodology was developed in order to detect low levels of 34 antibiotics. In the medical center, the main prescribed antibiotic (amoxicillin) was weakly found in effluents. Along the continuum, contamination of water by antibiotics decreased from 160 μg.L−1 (cefotaxime) in hospital effluents to 1 ng.L−1 (ofloxacin) in the river. These concentrations were too low to exert a selective pressure (mg.L−1) on antibiotic-resistant bacteria. In the same samples, occurrence of antibiotic-resistant E. coli and those harboring a class 1 integrons was significantly (p-value < 0.001) decreased along the continuum. Among Enterococcus populations, E. faecium was mainly isolated (from 89 to 98 %). All E. faecium isolates from medical center effluents were multiple antibiotic resistant, containing erm(B) and mef(A) genes, and belonged to the hospital-adapted clonal complex 17 (CC17). The relative proportion of CC17 decreased in favor of other subpopulations, less resistant to antibiotics. In water, only persistent compounds were found (quinolones, macrolides, sulfonamides), but they did not correspond to the major resistances in E. coli and Enterococcus (penicillins, tetracyclines).