y of Ireland, Department of Biology, Maynooth, Co Kildare Ireland

Impact of streptomycin applications on antibiotic resistance in apple orchards

The Federal Office for Agriculture (FOAG) authorized the use of streptomycin to fight fire blight under controlled conditions in 2008 with the provison that the development of antibiotic resistance in the treated plots is monitored. Agroscope in Wädenswil thus performed the first study to quantitatively analyze the influence of streptomycin use in agriculture on the abundance of the mobile streptomycin and tetracycline resistance genes (strA, strB, aadA, tetB, tetM, tetW) and the insertion sequence IS1133. Furthermore, the effect of the streptomycin treatment on the bacterial community structure was assessed. Flowers, leaves and soil were collected from three streptomycin-treated orchards in 2010, 2011 and 2012. The abundance and distribution of the resistance genes was analyzed at different time-points and included as a function of the treatment. The mobile antibiotic resistance genes were detected prior to streptomycin treatment in almost all samples, indicating the presence of these genes in nature. Statistically significant increases in the resistance gene abundance were occasional, inconsistent and not reproducible from one year to the next. Analysis of the bacterial community in soils from orchards with or without streptomycin treatment revealed no statistically significant or constant alterations. We conclude that the application of streptomycin in these orchards led neither to an increase in streptomycin or tetracycline resistance gene abundance nor to a negative impact on the bacterial community.

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