Efficacy of agricultural disinfectants on biofilms of the bacterial ring rot pathogen, Clavibacter michiganensis subsp. sepedonicus
Susceptibility of biofilms of Clavibacter michiganensis subsp. sepedonicus, the causal agent of bacterial ring rot of potato, to three common agricultural disinfectants was tested. The MBECTM assay device was used to evaluate optimum parameters for growing artificial biofilms. These conditions were determined to be 7 days of growth at 23°C in a yeast extract-glucose-mineral salts medium. As expected, the bacteria in the biofilm state were more resistant to disinfection by chemical treatment with sodium hypochlorite, quaternary ammonium, and hydrogen peroxide when compared with planktonic cells. Artificial biofilms were also grown on five different surface materials typically found in commercial potato storage facilities (concrete, mild steel, rubber, polycarbonate and wood) using the BESTTM assay device to test the effect of surface type on biofilm susceptibility to disinfection. Sodium hypochlorite was the most effective disinfectant on the wood surface and hydrogen peroxide was best on the mild steel surface. Efficacies of the various disinfectants were not significantly different on concrete, rubber and polycarbonate surfaces. When artificially grown biofilms and those grown naturally in potato tissue were transferred to, and dried onto, coupons of the different surface materials, they were significantly more difficult to inactivate than in situ grown biofilms. The resistance of plant pathogenic bacteria in the biofilm state, particularly when spread and dried onto surfaces of agricultural machines and other equipment, to commonly used disinfectants, has important implications for disease control strategies that depend largely on strict sanitary and hygienic practices.