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genetic transfers would therefore be possible at high cellular densities,
likely to be reached in deposition zones of antibiotic-resistant bacteria,
such as mudflats, periphytons, and indeed filter feeders, chronically
exposed to both contamination by antibiotics and antibiotic-resistant
bacteria.
Depending on human and agricultural activity in the watershed, the
microbial resistome in estuarine mudflats becomes an enriched
environmental resistome, where the dynamics of the horizontal gene
transfer between bacteria of different phylums are still poorly
understood. For the next decades, whereas the consequence of the
expected increase of the demography will be accompanied by an
increase in prescriptions for antibiotics, the likelihood of the
retrotransfer of genes from autochtonous microorganisms to strains
clinical strains, on an unknown scale of space and time, will be a
major environmental concern with decisive consequences in public
health [WEL 13].
2.3. Fate of contamination by antibiotics and antibiotic-resistant
bacteria in estuary environments: Seine Estuary case study
2.3.1.
The Seine Estuary: one of the most anthropized estuaries in
Europe
Chemical and microbiological contamination of coastal areas and
estuaries reflects the anthropogenic pressure exerted on their
catchments. On the continental shelf of northwest Europe, the Seine
estuary is the outlet of a drainage basin of 79,000 km
2
, where 30% of
the French population, 40% of the economic activity and 30% of
national agricultural activity is concentrated. The microbiological
quality of the Seine estuary waters is poor, and is mainly dominated,
in high flow periods, by the upstream inputs of the WWTP, which
treats the waste water from Paris and its suburbs (about five million
inhabitants), and is located 120 km unpstream of the Dam of
Poses (Figure 2.2). However, in periods of low flow, intra-estuary
supplies are predominant with a contamination from tributaries close
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