Listeria are short, Gram-positive non-sporeforming bacilli that invade host cells to exist as intracellular parasites. The traditional species (Listeria sensu stricto) can grow at temperatures as low as 4 C and are motile when grown at 25 C but not at 37 C. Listeria are catalase positive and ferment acids but do not generate gas. They are among the most common causes of serious diseases in animals, and some species are of growing importance to human health due to infections through contaminated foods, including raw milk, dairy, and meats.
Listeria ivanovii is commonly found as a normal inhabitant of the gastrointestinal tract of at least 40 species of mammals and vertebrates. It is an important pathogen for mice, sheep, and possibly humans. causes infections of numerous organ systems in many domestic and wild animals, most notably meningtis/encephalitis and abortion in ruminants. Human infections are relatively rare events.