Listeria is a genus of bacteria that acts as an intracellular parasite in mammals. As of 2024, 28 species have been identified. The genus is named in honour of the British pioneer of sterile surgery Joseph Lister. Listeria species are Gram-positive, rod-shaped, and facultatively anaerobic, and do not produce endospores.
The major human pathogen in the genus is L. monocytogenes. Although L. monocytogenes has low infectivity, it is hardy and can grow in a refrigerator temperature of 4 °C (39.2 °F) up to the human body temperature of 37 °C (98.6 °F). It is the usual cause of the relatively rare bacterial disease listeriosis, an infection caused by eating food contaminated with the bacteria. The overt form of the disease has a case-fatality rate of around 20–30%. Listeriosis can cause serious illness in pregnant women, newborns, adults with weakened immune systems and the elderly, and may cause gastroenteritis in others who have been severely infected. The incubation period can vary from three to 70 days. The two main clinical manifestations are sepsis and meningitis, often complicated by encephalitis, a pathology unusual for bacterial infections.
