Despite our increasing knowledge about properties and occurrence of Listeria monocytogenes in the food chain, this bacterium remains a serious hazard. It can cause a mild non-invasive illness (called listerial gastroenteritis) or a severe, sometimes life-threatening, illness (called invasive listeriosis) with a case-fatality rate ranging from 20 to 30 percent. Listeria monocytogenes is ubiquitously found in the environment. Sources of this bacterium in foods include ingredients/raw foods, processing aids, contact surfaces, and plant environments.  In the case of food contamination with L. monocytogenes, products that pose a high risk of being associated with listeriosis are those that support growth of L. monocytogenes, but do not undergo heating before consumption (ready-to-eat, RTE). Foods that do not support growth of L. monocytogenes, on the other hand, pose a low risk. Such foods have intrinsic or extrinsic factors to prevent the growth of L. monocytogenes (e.g., pH ≤ 4.4, Aw ≤ 0.92, or other factors). For many RTE foods, contamination of foods with L. monocytogenes can be avoided; e.g., through the application of good manufacturing practices (including controls on ingredients, plant hygiene), the use of validated heat treatments, listericidal and listeristatic processes or ingredients, segregation of foods that have been heated from those that have not, sanitation, and, overall, by avoiding processing or production failure. In addition, prevention of outgrowth in a food is an effective strategy to safeguard food safety. This session covers the occurrence of L. monocytogenes in > 50 food production plants, the efficacy of cleaning and sanitation agents to reduce the levels of L. monocytogenes, and an example of growth inhibition of L. monocytogenes in a RTE food, as demonstrated by challenge studies and evaluation of antimicrobial compounds naturally present.

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