LESS Plus Medium Irradiated

Listeria monocytogenes, described first in 1926 by Murray, Webb and Swann, is an extensive problem in public health and food industries. This organism has the ability to cause human illness and death, particularly in immunocompromised individuals and pregnant women. Epidemiological evidence from outbreaks of listeriosis indicates the principle route of transmission is via the consumption of foods contaminated with Listeria monocytogenes. Implicated vehicles of transmission include meat, eggs, chicken, vegetables, and dairy products. Listeria spp. are ubiquitous in nature, present in a wide range of unprocessed foods and in soil, sewage, and river water. Certain strains of Listeria spp. are able to survive the manufacturing and ripening processes in dairy products. Listeria spp. grow over a pH range of 5.0 – 9.6 and survive in food products with pH level outside these parameters. Listeria spp. are microaerophilic, Gram-positive, asporogenous, non-encapsulated, non-branching, short, motile rods. Motility is pronounced at 20°C for Listeria.