DNase I and proteinase K impair Listeria monocytogenes biofilm formation and induce dispersal of pre-existing biofilms

Current sanitation methods in the food industry are not always sufficient for prevention or dispersal of Listeria monocytogenes biofilms. Here, we determined if prevention of adherence or dispersal of existing biofilms could occur if biofilm matrix components were disrupted enzymatically. Addition of DNase during biofilm formation reduced attachment (< 50% of control) to polystyrene. Treatment of established 72 h biofilms with 100 μg/ml of DNase for 24 h induced incomplete biofilm dispersal, with < 25% biofilm remaining compared to control. In contrast, addition of proteinase K completely inhibited biofilm formation, and 72 h biofilms—including those grown under stimulatory conditions—were completely dispersed with 100 μg/ml proteinase K. Generally-regarded-as-safe proteases bromelain and papain were less effective dispersants than proteinase K. In a time course assay, complete dispersal of L. monocytogenes biofilms from both polystyrene and type 304H food-grade stainless steel occurred within 5 min at proteinase K concentrations above 25 μg/ml. These data confirm that both DNA and proteins are required for L. monocytogenes biofilm development and maintenance, and that these components of the biofilm matrix can be targeted for effective prevention and removal of biofilms.