Polymerase Chain Reaction for Detection of Listeria monocytogenes

There are several species of Listeria , but only Listeria monocytogenes has been identified as the principal pathogen in humans and animals. L. monocytogenes is a ubiquitous Gram-positive bacterium responsible for an uncommon but potentially serious infection in humans who ingest contaminated food. The symptoms of listeriosis in humans can include meningitis, encephalitis, and sepsis. In some cases fatalities have occurred. The major risk groups are pregnant women, young children, elderly people, and the immune compromised. L. monocytogenes has been shown to survive in a wide range of environmental conditions including salt concentrations of up to 10%, temperatures as low as 4�C, and in a variety of food products (1 ). According to the Centers for Disease Control (CDC), between 1988 and 1990, there was an annual incidence of 7.4 cases per 1 million population in the surveillance areas. Of these cases, 23% of the individuals died and of that number 33% were pregnant women. There are at least 16 serotypes of L. monocytogenes , which are identified by a serological grouping of the five heat-labile flagellar antigens and the 14 carbohydrate-containing heat-stable antigens (2 ). Listeria are ubiquitous in nature, being found in soil, sewage, river water, vegetable matter, silage, other animal fodder, insects, the human intestines, raw milk, and kitchen premises (3 ).