5 Antibiotics and Bacterial Antibiotic Resistance
5.1 Context
Since the first synthesis of antibiotics in 1940s, numerous molecules have been
discovered, and nowadays there are about 10,000 antibiotics on the market
[62]. Although these molecules have reduced mortality from infectious diseases
and thus increased life expectancy, the use of these molecules has also induced
environmental contamination. The first detection of pharmaceuticals in surface
waters occurred in 1976 with the detection of clofibric acid and salicylic acid in a
lake in Nevada. Since then, almost all categories of pharmaceutical substances have
been found in surface waters [63].
The actual impact of antibiotic discharge on ecosystem functioning is still
unknown. For instance, the concentrations of antibiotics observed in water (on the
order of ng L
À1 ) are too low to affect the growth of fish such as Japanese medaka
(EC50 100 mg L
À1 for sulfonamides) or algae (in the range of 0.1–1 mg L
À1 ). At the
microbial community level, concentrations measured in situ are below the minimum
inhibitory concentration required to exert selection pressure on environmental
microorganisms (on the order of mg L
À1 ); however, subinhibitory concentrations
may promote mutagenesis or modify gene expression and may significantly influence bacterial physiology [64–67].
Since 2003, several studies of the PIREN-Seine programme have targeted pharmaceutical residues, particularly antibiotics. The main objectives of these studies are
to determine the pathways of contamination in the natural environment, the environmental behaviour of these substances and the potential risk to ecosystems.
5.2 Sources of Antibiotics in the Seine Watershed
In rural areas, no contamination by antibiotics is observed in forest streams, but the
contamination appears when streams flow through agricultural or breeding areas.
Tamtam et al. [68] measured a concentration of 20 ng L
À1 of enrofloxacin in a small
river (the Blaise). This compound is exclusively used in veterinary medicine, and
therefore the finding shows the contribution of this use to river contamination.
Antibiotic inputs to rivers in agricultural/rural areas may also come from their use
in fish farming [69]: in such farms, antibiotics may be mixed with fish food and
dispersed directly into the breeding ponds. Thus, the presence of fish farms may
generate the discharge of antibiotics into rivers. During antibiotic treatment in fish
farms, flumequine was quantified as high as 7 μg L
À1 in the effluent of the treatment
pond, and 2 days after the end of the treatment, flumequine concentrations were
below the limits of quantification. However, 20 days later, this molecule was still
measurable in the sediments of the river downstream of the fish farm discharge [68].
370
P. Labadie et al.
5.1 Context
Since the first synthesis of antibiotics in 1940s, numerous molecules have been
discovered, and nowadays there are about 10,000 antibiotics on the market
[62]. Although these molecules have reduced mortality from infectious diseases
and thus increased life expectancy, the use of these molecules has also induced
environmental contamination. The first detection of pharmaceuticals in surface
waters occurred in 1976 with the detection of clofibric acid and salicylic acid in a
lake in Nevada. Since then, almost all categories of pharmaceutical substances have
been found in surface waters [63].
The actual impact of antibiotic discharge on ecosystem functioning is still
unknown. For instance, the concentrations of antibiotics observed in water (on the
order of ng L
À1 ) are too low to affect the growth of fish such as Japanese medaka
(EC50 100 mg L
À1 for sulfonamides) or algae (in the range of 0.1–1 mg L
À1 ). At the
microbial community level, concentrations measured in situ are below the minimum
inhibitory concentration required to exert selection pressure on environmental
microorganisms (on the order of mg L
À1 ); however, subinhibitory concentrations
may promote mutagenesis or modify gene expression and may significantly influence bacterial physiology [64–67].
Since 2003, several studies of the PIREN-Seine programme have targeted pharmaceutical residues, particularly antibiotics. The main objectives of these studies are
to determine the pathways of contamination in the natural environment, the environmental behaviour of these substances and the potential risk to ecosystems.
5.2 Sources of Antibiotics in the Seine Watershed
In rural areas, no contamination by antibiotics is observed in forest streams, but the
contamination appears when streams flow through agricultural or breeding areas.
Tamtam et al. [68] measured a concentration of 20 ng L
À1 of enrofloxacin in a small
river (the Blaise). This compound is exclusively used in veterinary medicine, and
therefore the finding shows the contribution of this use to river contamination.
Antibiotic inputs to rivers in agricultural/rural areas may also come from their use
in fish farming [69]: in such farms, antibiotics may be mixed with fish food and
dispersed directly into the breeding ponds. Thus, the presence of fish farms may
generate the discharge of antibiotics into rivers. During antibiotic treatment in fish
farms, flumequine was quantified as high as 7 μg L
À1 in the effluent of the treatment
pond, and 2 days after the end of the treatment, flumequine concentrations were
below the limits of quantification. However, 20 days later, this molecule was still
measurable in the sediments of the river downstream of the fish farm discharge [68].
370
P. Labadie et al.