Listeria monocytogenes: biofilm formation and persistence in food-processing environments

Listeria monocytogenes is ubiquitous in nature and a major concern for the food industry, since it is the causal agent of the serious foodborne illness listeriosis. This organism can be introduced through many routes to food-processing environments and may become established on food-processing equipment. Subsequently, food products may become contaminated during processing. In addition, the bacterium can grow at refrigeration temperatures. Biofilms are regarded as important with respect to the survival and growth of microorganisms in the food industry. Microorganisms growing in biofilms are protected against cleaning and disinfection and are difficult to eradicate. Listeria monocytogenes may grow in biofilms that protect them against environmental stress and can be isolated from surfaces after cleaning and disinfection. For each individual food-processing plant, a limited number of clones of L. monocytogenes may become established and persist for years. Persistent strains adhere to surfaces and form biofilms more readily compared to sporadically found strains, suggesting that adherence to surfaces is important for survival and persistence of L. monocytogenes in food-processing environments. Listeria monocytogenes can adhere to all the materials commonly used in the food industry. In biofilms L. monocytogenes is significantly more resistant to disinfection than its free-living counterparts and thick, complex biofilms are more difficult to remove than adherent single cells of L. monocytogenes . Several novel approaches to avoid adhesion of L. monocytogenes have been proposed, but high costs, practical difficulties or resistance problems limit their practical use. Despite considerable research on the adhesive properties and resistance of L. monocytogenes enabling its survival in the food production environment, a final solution for avoiding establishment of the bacterium has not yet been found.