Listeria monocytogenes: Growth in biofilms in the food industry

Listeria monocytogenes is an important foodborne pathogen not because it causes large numbers of symptomatic cases but because of its relatively high case-fatality rate (20-30%). Listeriosis appears to be primarily a foodborne infection and is particularly a problem on foods that are not cooked, including ready-to-eat (RTE) meats, soft cheeses, and unpasteurized dairy products, as well as vegetables. Thermal processing of milk and meat products will destroy L. monocytogenes but post-processing contamination does occur. L. monocytogenes that contaminates foods may originate in soils from farms, in slaughtering facilities, in food processing plants and other equipments used in food manufacture. Elimination of Listeria from many environmental sources can be challenging because of the resistant, persistent biofilms formed by this microorganism. Bacterial biofilms are generally described as surface-associated bacterial communities forming microcolonies surrounded by a matrix of exopolymers. Biofilm formation can be separated into four sequential steps: (i) conditioning of the surface, (ii) initial adherence, (iii) physical irreversible adherence that involves the production of exopolymers that fix the cells, and (iv) growth of the microorganisms, which form microcolonies, and coaggregation leading to establishment of the biofilm. Such structures are dynamic systems in which cells grow, die, and/or are released, allowing contamination of other surfaces. Moreover, biofilms confer to L. monocytogenes a greater resistance to antimicrobial agents and they allow microorganisms to resist to environmental changes and cleaning/disinfection treatments. In the following, through an up-to-date review of (personal and non) published data, the growth of L. monocytogenes in biofilm in the food industry will be discussed.