Vulnerability and Resilience of Estuaries to Contamination by Antibiotics and Antibiotic-Resistant Bacteria: a Challenge for the Next Decade - Vulnerability of Coastal Ecosystems and Adaptation - page 67

molecules (or their metabolites) can be reached; (2) a transfer of
resistance genes from the microbial community to native species,
followed by a retrotransfer to humans via pathogenic strains is possible,
even if the probability is low.
Antibiotics have a unique character: with emerging contaminants of
aquatic environments, their intensive use in human and animal medicine
is also responsible for the emergence of antibiotic-resistant bacteria
[AAR 05, SEV 02]. Since the 1950s, which saw the beginning of the
large-scale use of antibiotics, pathogenic bacteria, initially sensitive to
antibiotics, have very rapidly acquired resistance mechanisms, some of
which were acquired via environmental bacteria. One example, the
pandemic of the extended-spectrum beta-lactamases (ESBLs), whose
therapeutic consequences are severe, is a consequence of a genetic
transfer from environmental bacteria (e.g, CTX-M from Kluyvera spp,
Poirel et al ., 02). Subsequently, the notion of an environmental
resistome has been introduced and defined as the group of resistant
genes in a given environment. Thus, in an aquatic environment, the
resistome, i.e. all the resistance genes in the genome of environmental
bacteria, is enriched with the genes from bacteria of human and animal
origin that are discharged into this environment [WEL 13, WRI 07].
Controlling the increase of bacterial resistance to antibiotics,
recognized as a major problem in public health by the World Health
Organization ([OMS 01], Millennium Ecosystem Assessment ,
http://milleniumassessment. org), will be one of the leading challenges
of the next decades to come.
2.2. Bacterial antibiotic resistance: a global ecological process
Bacterial resistance to antibiotics is a complex ecological
phenomenon which should be investigated, by considering the
circulation of micro-organisms and the corresponding resistance genes
within the four major ecosystems: humans, animals, soil and water
(Figure 2.1). Prescribed in human and veterinary medicine depending
on the legislation in force 2 , antibiotics or their metabolites are
2 The prescription antibiotics as an additive in animal food is forbidden by European
Union (EU) regulations (rule no. 1831/2003).