Listeria monocytogenes is a gram-positive, non-spore forming, rod-shaped, facultative intracellular bacterium that affects animals and humans, including poultry. Infection occurs when ingested bacteria cross the intestinal barrier and disseminate to various organs and the bloodstream, leading to the disease known as listeriosis. It manifests as encephalitis, meningitis, and septicemia.
Unlike many other common foodborne diseasecausing bacteria, Listeria can survive and multiply at low temperatures, and usually found in refrigerators. Eating contaminated food with high numbers of Listeria is the main route of infection. Foods which are known to have a long shelf-life under refrigeration are most commonly associated with listeriosis outbreaks.
Listeria are ubiquitous in nature and found in soil, water and animal digestive tracts. Vegetables may be contaminated through soil or the use of manure as fertilizer. Rich sources include soil, manure/sewage, farm slurry, sludge, silage, animal feed, water and excreta/faeces of mammals and birds. Vegetables and fruits may be contaminated through soil or the use of manure as fertilizer.