Wednesday, March 10, 2010

Increasing Resistance in Soil Microbes in The Netherlands

Despite improved waste management practices and bans on antibiotic growth promoters, DNA isolated from soil microbes in the Netherlands shows that antibiotic resistant genes (ARGs) have become progressively more common in the past 70 years. A recent study by Danish and English scientists, published in Environmental Science and Technology, examined 18 different ARGs in five long-term soil series from different rural areas in The Netherlands, collectively spanning 1940-2008. After normalizing the ARG levels to cover a common time period for all of the series, 78 percent of the ARGs showed an increasing trend over time. Four out of the five sites displayed consistently increasing ARG levels. These increases were most pronounced for resistance to tetracyclines, but were also present for the three other classes of antibiotics examined: extended spectrum beta-lactamases, erythromycins, and glycopeptides. This figure shows these relative increase in genes encoding for resistance to three different antibiotics over the period studied.

These findings are signficant because antibiotic-resistant bacteria are capable of conferring resistance to other potentially disease-causing bacteria in the envrionment. Resistance in soil microbes could impact humans through food consumption or through the water supply and make human pathogens more dangerous and difficult to treat. It is also interesting that these increases in resistance occured in spite of improvements to waste management that were made in The Netherlands in the late 1970's, and bans on antibiotics as growth promoters in the European Union that were implemented between 1997 and 2006, suggesting that more efforts need to be made to both prevent and protect ourselves from environmental reservoirs of resistance.

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