Listeria monocytogenes is a Gram-positive, motile bacterium and the causative agent of listeriosis, a serious foodborne illness particularly dangerous for pregnant women, newborns, the elderly, and immunocompromised individuals. It is a facultative intracellular pathogen found in soil, water, and a broad range of food products, capable of growing at refrigeration temperatures. Outbreaks are frequently associated with contaminated ready-to-eat foods such as deli meats, soft cheeses, and raw vegetables.