Kasugamycin (Ks) is an alternative to the use of streptomycin for the control of bacterial plant diseases. However, there is a concern that Ks application in orchards will select for Ks resistance that could be linked with other resistance genes that are active against antibiotics used in human medicine. To monitor for this, we assessed the effect of the use of Ks in orchard systems on the level of resistance to Ks and to five other antibiotics used in human medicine. Two sets of leaf and soil samples were collected (treated and non-treated with Ks) from 41 fruit tree orchards throughout the United States in 2015 and 2016. Samples were processed in the laboratory and dilution plated onto King’s B medium with or without Ks amendment. Bacterial population sizes were determined per sample and Ks-insensitive gram-negative isolates were further evaluated for multi-drug resistance. No differences were observed in Ks-insensitive populations or levels of resistance to the five other antibiotics tested between Ks treated vs. non- treated sites.Erwinia amylovora, the causal agent of fire blight of apple, is disseminated in ooze droplets, which consist of bacterial cells embedded in at least two exopolysaccharides, levan and amylovoran. Based on previous observations, we hypothesized that a reduction in levan production would result in a decrease in ooze droplets. To study this, E. amylovora strains with variation in levan production were evaluated for ooze production in growth chamber and field trials. Strains with a reduction in levan showed reduced ooze production in shoots in growth chamber studies. However, no differences in ooze production were observed in field trials.
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