Listeria monocytogenes IntroductionListeria monocytogenes, a gram-positive motile rod, is an opportunistic foodborne pathogen capable of causing listeriosis in humans. Listeriosis includes manifestations of septicemia, meningitis, pneumonia and encephalitis. L. monocytogenes is also implicated in miscarriages, stillbirths, and preterm births for pregnant women. L. monocytogenes is a tough bacterium resistant to freezing, drying and heat; most strains proved to be pathogenic. It is hypothesized that 1-10% of humans are intestinal carriers of L. monocytogenes. Over 37 mammal species, including wild and domestic animals, are capable of infection and transmission of L. monocytogenes. Vast environmental reservoirs for L. monocytogenes include soil, water, vegetation, sewage, silage, and the intestinal tracts of various animals.Encounter:L. monocytogenes is transmitted through ingestion of contaminated food or water. The bacterium is associated with raw milk, cheeses, ice cream (particularly soft varieties), raw vegetables, fermented raw meat sausages, raw and cooked poultry, raw meats, and raw and smoked fish. It is capable of growing at temperatures as low as 3°C allowing multiplication in refrigerated foods, making L. monocytogenes infection particularly difficult to avoid. The infectious dose has not been determined, but is believed to vary with the susceptibility of the individual. There may be fewer than 1000 bacteria in the immunocompromised individual. Entry, multiplication and diffusion:L. monocytogenes initially enters the organism through the gastrointestinal tract but is capable of infecting the blood through monocytes, macrophages and polymorphonuclear leukocytes. The bacterium is also capable of infecting the nervous system, the elderly and people with other serious medical problems. Worldwide: Approximately 2,500 cases of listeriosis are reported worldwide each year. United States. This includes 500 preventable deaths. Outbreaks of L. monocytogenes still occur worldwide. As recently as 2002, contaminated turkey meat caused an epidemic in the United States along the East Coast, and contaminated cheese caused an epidemic in British Columbia. Over the past two decades, outbreaks have involved contaminated chocolate milk, shrimp, deli meats and cheese. An outbreak in California in 1985 was due to contaminated Mexican cheese. This epidemic led to numerous stillbirths resulting in cheese monitoring by the FDA. Fortunately, according to a study conducted by the U.S. Department of Health and Human Services, L. monocytogenes infections decreased by 35 percent from 1996 to 2002.