Burkholderia glumae R1 (R1) and R2 (R2) resistant to oxolinic acid (OA) at 100μg/ml were isolated on a PS agar (PSA) medium containing OA and from rice seedlings grown from OA-treated seeds which had been inoculated with
B. glumae Pg-4 (Pg-4) susceptible to OA, respectively. R1 and R2 were also resistant to nalidixic acid and norfloxacin. R1 grew on a PSA medium containing OA (100μg/ml) in the presence of EDTA-Fe (1000μg/ml), but R2 did not grow on the medium. These results indicate that
B. glumae isolates resistant to OA are cross-resistant to quinoline derivatives, and that the decrease in the susceptibility of R2 to the chemical results from the reduction in bacterial cell membrane permeability to the chemical. When R1-inoculated rice seeds were treated with OA, R1 grew rapidly in the rice seedlings after seed soaking and caused severe rotting of the seedlings. However. R1 did not grow rapidly in OA non-treated seedlings, and only a few seedlings rotted. When Pg-4-inoculated rice seeds were treated with OA, OA-resistant
B. glumae accounted for 10% of the
B. glumae population in the seedlings at the time of transplanting. However, when the seedlings were transplanted into a paddy field and treated with OA at the heading stage, the population of resistant bacteria in the transplanted rice plants was less than 1×10
2cfu/g, the minimum limit for detection of bacteria. No resistant bacteria were isolated from the grains of mature rice plants. Nor could we isolate OA-resistant
B. glumae from rice plants inoculated with Pg-4 at heading. Experiments results indicate that OA-resistant
B. glumae grows rapidly in seedlings and rots them, but only when seeds are infected with a high density of the OA-resistant bacteria and are treated with OA. The resistant bacteria do not have the ability to survive in the paddy field.
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