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 7days of growth at 23 degrees 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. ResumeLa sensibilite des biofilms de Clavibacter michiganensis subsp. sepedonicus, l'agent causal de la pourriture du cerne chez la pomme de terre, a trois desinfectants agricoles courants a ete testee. Le biotest MBECTM a ete utilise pour evaluer les parametres optimaux relatifs a la croissance de biofilms artificiels. Ces conditions ont ete etablies a sept jours de croissance a 23 degrees C sur un milieu a base d'extrait de levure, de glucose et de sels mineraux. Comme nous nous y attendions, lorsque comparees aux cellules planctoniques, les bacteries a l'etat de biofilms etaient plus resistantes a la desinfection chimique effectuee avec de l'hypochlorite de sodium, de l'ammonium quaternaire et du peroxyde d'hydrogene. Des biofilms artificiels ont egalement ete cultives sur cinq differents materiaux de surface trouves generalement dans les entrepots commerciaux pour pommes de terre (beton, acier doux, caoutchouc, polycarbonate et bois). Ces derniers ont ete evalues avec le biotest MBECTM afin d'estimer l'influence du type de surface sur la sensibilite des biofilms a la desinfection. L'hypochlorite de sodium s'est revele le desinfectant le plus efficace sur le bois, et le peroxyde d'hydrogene s'est avere le plus efficace sur l'acier doux. Les taux d'efficacite des divers desinfectants n'etaient pas significativement differents sur les surfaces en beton, en caoutchouc et en polycarbonate. Quand les biofilms cultives artificiellement et ceux cultives naturellement sur des tissus de pomme de terre ont ete transferes, et seches, sur des coupons des differents materiaux, ils etaient significativement plus difficiles a inactiver que les biofilms cultives in situ. La resistance des bacteries pathogenes, a l'etat de biofilms, aux desinfectants utilises couramment, particulierement lorsque ces biofilms sont appliques et seches sur la machinerie agricole et les autres equipements, a d'importantes implications quant aux strategies de lutte contre la maladie qui dependent en grande partie de mesures sanitaires et hygieniques strictes.