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Degradation of sulfonamides as a microbial resistance mechanism
Este artĂculo contiene 9 páginas, 5 figuras, 1 tabla.Two of the main mechanisms of bacterial resistance to sulfonamides in aquatic systems, spread of
antibiotic resistance genes (ARG) among the microbial community and in-situ bacterial sulfonamide
degradation, were studied in mesocosms experiments using water and cobble biofilms from upstream
(pristine waters) and downstream (polluted waters) from the Llobregat river, NE Iberian Peninsula.
Mesocosms were prepared at two different concentrations (5000 ng/L and 1000 ng/L) of sulfonamides
antibiotics (sulfamethazine and sulfamethoxazole). Concentrations of ARG, nutrients, sulfonamides and
their degradation products were measured during the time course of the experiments. Sulfonamides
were efficiently degraded by the biofilms during the first four weeks of the experiment. The abundance
of ARG in biofilms sharply decreased after addition of high concentrations of sulfonamides, but this was
not observed in the mesocosms treated with low concentrations of sulfonamides. Sulfonamide degradation
was faster in polluted waters and at high concentrations of sulfonamide (and lower ARG abundances),
suggesting that both degradation and ARG are two complementary resistance strategies
employed by the microbial community. This study shows that microbial degradation of antibiotics is an
efficient resistance mechanism coupled with the presence of ARG, and suggests that in situ degradation
prevails at high concentrations of antibiotics whereas physiological adaptation by ARG spread would be
more important under relatively lower concentrations of antibiotics.This work has been supported by Marie Curie ActionsdIntra-
European Fellowships (IEF), project number 275863 and by the
Spanish Ministry of Economy and Competitiveness project DARKNESS
CGL2012-32747 to E.O.C.Peer reviewe