Environmental Monitoring of Antibiotic Resistance and Impact of Streptomycin Use on Orchard Bacterial Communities

Streptomycin use to control fire blight is a contentious issue in Europe and has been permitted only as an emergency stop-gap measure. Swiss approval has been contingent upon continued environmental impact study. Annual monitoring since first use in 2008, has demonstrated widespread resistance in plant/soil bacterial communities regardless of streptomycin exposure, and confirmed lack of pathogen resistance in Switzerland. Thus far, no effect has been observed for streptomycin applications on indigenous bacterial communities (short-or long-term effects) inhabiting the phylosphere (flowers, leaves, fruit) or soil. Using RISA to compare effects of 3x streptomycin treatment vs. water or biocontrol (yeast, BlossomProtect) treatment on total (culturable/nonculturable) bacterial community biodiversity - no effect of streptomycin was observed at any time point, from 1 day after application through apple harvest. Even under worst-case trials in the orchard and laboratory, soil drenching with up to 100-times standard orchard canopy application rates found no effect on bacterial communities. The only consistent effect on bacterial community biodiversity was actually observed on fruit from biocontrol-treated plots.