Listeria monocytogenes is a Gram-positive, non-spore forming, rod-shaped, facultative bacterium. Listeriosis refers to the disease caused by infection with L. monocytogenes. It manifests as encephalitis, meningitis, and septicemia.
Transmission: Unlike many other common foodborne diseases causing 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. Food most often associated with listeriosis outbreaks include foods with a long shelf-life under refrigeration
Survival in environment: Listeria are widespread and truly ubiquitous in nature and commonly found in temperate zone. Rich sources include soil, manure/sewage, farm slurry, sludge, silage, animal feed, water and excreta/faeces of mammals and birds. They are also isolated from walls, floors, drains, decaying vegetation, rivers, pasture herbage, factory effluents, etc. of farms and other environments. A study on listeriosis showed that, at 5 °C, the organism survives for 13, 16, 12 and 12 years in milk, brain, feces and silage, respectively.
Hosts: Dairy cows serve as the main reservoir and high levels of the pathogen occurs in animals fed with improperly fermented silage contaminated by growth on manure-fertilized soils.