L. monocytogenes was first described by E.G.D.Murray in 1926 based on six cases of sudden death in young rabbits. Murray referred to the organism as Bacterium monocytogenes before J.H. Harvey Pirie changed the genus name to Listeria in 1940. Although clinical descriptions of L. monocytogenes infection in both animals and humans were published in the 1920s, not until 1952 in East Germany was it recognized as a significant cause of neonatal sepsis and meningitis. Listeriosis in adults would later be associated with patients living with compromised immune systems, such as individuals taking immunosuppressant drugs and corticosteroids for malignancies or organ transplants, and those with HIV infection.
L. monocytogenes has three distinct lineages with differing evolutionary histories and pathogenic potentials. Lineage I strains contain the majority of human clinical isolates and all human epidemic clones, but are underrepresented in animal clinical isolates. Lineage II strains are overrepresented in animal cases and underrepresented in human clinical cases as well as more prevalent in environmental and food samples. Lineage III isolates are very rare but significantly more common in animal isolates than human.
Listeriosis is a serious infection caused by eating food contaminated with the bacterium called Listeria monocytogenes. Although there are other types of Listeria, most cases of listeriosis are caused by Listeria monocytogenes. Listeria is found in soil and water. Vegetables can become contaminated from the soil or from manure used as fertilizer. Animals can carry the bacterium without appearing ill and can contaminate foods of animal origin, such as meats and dairy products. Listeria has been found in a variety of raw foods, such as uncooked meats and unpasteurized (raw) milk or foods made from unpasteurized milk. Listeria is killed by pasteurization and cooking; however, in certain ready-to-eat foods, like hot dogs and cold cuts from the deli counter, contamination may occur after cooking but before packaging.
