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 66

of ng.L -1 ) are lower than the minimal inhibiting concentration
(MIC), thus, in theory, are not high enough to exert a selective
pressure on microorganisms (mg.L -1 ), or to affect the growth of algae
(0.1-1 mg.L -1 ), or fish such as the Japanese medaka (EC 50 100 mg.L -1
for sulfonamides) [SAN 10]. However, even subinhibiting
concentrations (0.25-0.9 CMI) can induce mutagenesis, interfer with

the bacterial quorum sensing signal transmission quorum sensing 1 , and
change the gene expression [DAV 06, GOH 02, GUL 11, KOH 10,
ZHA 13].

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Figure 2.1. Circulation of antibiotic-resistant microorganisms and antibiotics within
the four major ecosystems: human and animals under antibiotic treatment, soil and
water (see color section)

C OMMENTARY ON F IGURE 2.1.- Antibiotics prescribed in human and
veterinary medicine, and fecal antibiotic-resistant bacteria, are released
into the environment via urine and feces. Hence, effluent from WWTPs,
and surface run-off or soil leaching, will be the major sources of
contamination for waters and sediments. In an estuary environment, or
in rivers, antibiotic-resistant bacteria and the more stable molecules of
antibiotics are deposited on mudflats. The sediments then create an
environment where (1) subinhibiting concentrations of antibiotic
1 The group of regulatory mechanisms that control the coordinated expression of
certain bacterial genes within a single population of bacteria.