Listeria (Listeria monocytogenes) is a bacterium commonly found in soil and water, and in domestic animals. It can be responsible for a relatively uncommon but serious food-borne illness called listeriosis or listeria infection.
Listeriosis is caused by eating food contaminated with the bacteria. Types of food commonly contaminated by listeria include dairy products, fish, meat, and vegetables. Contamination can occur at any point in the farming, distribution, and food preparation process.