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 81

However, no simple relationship exists between the antibiotic-
resistance phenotypes of E. coli and Enterococcus , isolated in the
waters, with contamination of the environment by antibiotics and
prescriptions. The greatest antibiotic-resistance observed in E. coli
strains, isolated from the effluent of the retirement home, corresponds
to the most prescribed antibiotics: quinolones/ fluoroquinolones (42%)
and penicillins (38%). A significant proportion of the E. coli strains
are resistant to sulfonamides (24%), and tetracyclines (24%), even
though these antibiotics are not prescribed (Table 2.3(a)). The
presence of cassettes contained in the class 1 integrons are detected in
the genomes of 12/15 of the strains. If, for each antibiotic prescribed,
there is a corresponding resistance phenotype among the E. coli
strains released into the water, the phenotypes for multiresistance
observed are explained by the presence of integrons [CAM 10,
STA 12].
The epidemiological strains from the hospital, carrying specific
genetic supports (integrons, a gene for resistance to erm macrolides)
decreased along the continuum in favor of strains better adapted to the
environment (Figure 2.3). Thus, E. coli resistant to at least one
antibiotic and those carrying the class 1 integron, decreased
significantly along the continuum (p-value < 0.001) from the
retirement home effluents to the river (Table 2.2, Figure 2.3,
[OBE 12].
Among the Enterococci population, but mainly identified as
Enterococcus faecium , all isolates from the hospital were
multi-resistant, contained erm (B) and mef (A) and belonged to
hospital-adapted clonal complex 17(CC17) [LEC 13]. It decreases in
the treated effluent from the waste water treatment plant (19% and
17%) to reach 4% and 5% in the waters of the Risle. Interestingly,
while the proportion of Enterococcus faecium resistant to
erythromycin is greater than 70% along the the continuum, only the
hospital isolates exhibit a high level of resistance. The prevalence of
the erm (B) gene reaches 75% of the hospital isolates and only 6.7% of
the strains isolated in the river (Figure 2.4). Similarly, the occurrence