**3. Ecology and growth conditions of** *Listeria monocytogenes* **in the food chain**

*L. monocytogenes* are ubiquitous bacteria that can be found in different environments such as soil and water, and especially in food-manufacturing environments [20]. Many *Listeria* species have been isolated from soil, vegetation, sewage, water, animal feed, fresh and frozen meat including poultry, slaughterhouse wastes and the feces of healthy animals, including humans [21]. Animals have been found to be carriers of *L. monocytogenes*, hence the contamination of foods of animal origin, such as meats and dairy products [22].

*L. monocytogenes* can survive a low pH of 5.5 through a phenomenon known as the acid tolerance response (ATR), which causes cells to be more resistant in adverse acidic conditions [23]. The bacterium, which is notable for its persistence in food-manufacturing environments, is relatively salt-tolerant and is able to grow at refrigerator temperature, and is therefore often associated with the consumption of raw or minimally processed and often chilled RTE foods (e.g., soft and semi-soft cheese and smoked fish products), which are consumed without further processing [24, 25].
