Listeria monocytogenes (Listeria) is a pathogenic (disease-causing) bacterium that is food borne and causes an illness called listeriosis1. It is frequently overlooked as a possible cause of illness due to its unique growth capabilities. First, it is somewhat difficult for laboratories to grow, and when they do so, Listeria can be confused with common harmless contaminants and disregarded. Second, most bacteria grow poorly when temperatures fall below 40″F, while Listeria survives in temperatures from below freezing (20″F) to body temperature and it grows best at 0″F to 50″F,1 including the temperature range that we use for refrigeration. As a result, Listeria may be transmitted in ready-to-eat foods that have been kept properly refrigerated. Its ability to grow in such diverse environments is just one of the many challenges presented by this dangerous bacterium.

It is estimated that Listeria causes approximately 1,600 cases of listeriosis annually, resulting in 415 deaths.2
Where does Listeria monocytogenes come from?
There are many opportunities for contamination with Listeria during the process of food production because Listeria monocytogenes is ubiquitous in the environment.1 For example, it can be grown from wild and domestic animals, birds, insects, soil and wastewater, and vegetation. As it is a bacterium found in soil and vegetation, it is easily contracted and transmitted by herd animals. Listeria is found in grazing areas, stale water supplies, and poorly prepared animal feed. It can live in the intestines of humans, animals, and birds for long periods of time without causing infection. The bacterium is often isolated in cattle, sheep, and fowl, and is also found in dairy products, fruits, and vegetables.
1. Cossart P, Bierne H. The use of host cell machinery in the pathogenesis of Listeria monocytogenes. Curr Opin Immunol (England), Feb 2001, 13(1) p96-103.
2. FDA/CFSAN. 2003. Foodborne Pathogenic Microorganisms and natural Toxins Handbook: The ìBad Bug Book.” Center for Food Safety and Applied Nutrition, Food and Drug Administration, College park, MD. www.cfsan.fda.gov/~mow/intro.html.