Susceptibility of Listeria monocytogenes Biofilms and Planktonic Cultures to Hydrogen Peroxide in Food Processing Environments

Recent studies have indicated that Listeria monocytogenes formed biofilms on the surface of food processing equipment, and may survive sanitization treatments. The purpose of this study was to compare the susceptibility of L. monocytogenes grown in either a biofilm or planktonic culture when exposed to hydrogen peroxide (H2O2). Twelve strains of biofilm-forming L. monocytogenes and their planktonic counterparts were treated with various concentrations of H2O2 (1, 6, and 10%), and the cell survival was then determined at 10-min exposure intervals. When grown as a biofilm, L. monocytogenes was significantly more resistant to H2O2 than under planktonic culture conditions. Planktonic L. monocytogenes strains exhibited significantly different susceptibility to 1% H2O2. Equally interestingly, biofilms of the 12 L. monocytogenes strains also inhibited different survival rates after being treated with 6 and 10% H2O2. However, most of the biofilms recovered to a population of 2-9 log CFU/glass fiber filter (GFF) after a 24-h re-growth period. These results indicate that there was no significant correlation between the H2O2 resistance of biofilm- and planktonic-cultured cells, and suggest that different mechanisms for the resistance to sanitation or disinfection underly the persistence of certain strains in food-processing environments.