Listeria Monocytogenes

Listeria monocytogenes is a Gram-positive rod-shaped bacterium. It is the agent of listeriosis, a serious infection caused by eating food contaminated with the bacteria (Todar, 2008). The disease primarily affects older adults, pregnant women, new born, and adults with weakened immune systems. Babies can be born with listeriosis if their mothers eat contaminated food during pregnancy. However, healthy people may consume contaminated foods without becoming ill. Listeria monocytogenes is commonly found in soil and water. Animals can carry the bacterium without appearing ill and can contaminate foods of animal origin, such as meats and dairy products. When Listeria bacteria get into a food processing factory, they can live there for years, sometimes contaminating food products. Listeria is killed by cooking and pasteurization. However, in some ready-to-eat meats contamination may occur after factory cooking but before packaging. Other types of food that have been found to contain Listeria species are raw milk, raw vegetables, fish, poultry, and both fresh and processed meats. Unlike most bacteria, Listeria can grow and multiply in some foods in the refrigerator (Centers for Disease Control and Prevention, 2014). …show more content…
PALCAM medium was formulated by Van Netten et al.in 1989 to overcome the insufficient selectivity of media used in the past for the detection and enumeration of Listeria. Peptones and yeast extract favor the excellent growth of Listeria. Glucose and starch are the energy sources for microbial development. Sodium chloride maintains osmotic balance. Listeria hydrolyze esculin to glucose and esculetin, the latter compound forming a black complex with ferric ions supplied by ferric citrate (Biokar Diagnostics,