Listeria Monocytogenes is an acid tolerant, psychrotolerant, facultative anaerobic and salt tolerant bacterium. It is a short, gram positive, non-spore forming rod that is catalase positive.
It is found widely in soil and water, and virtually no fresh food is safe from L.monocytogenes contamination.
Fresh food can become contaminated at any stage during food growth or processing. Thus, meat, dairy products and fresh produce can become contaminated with this pathogen.
L.monocytogenes is an intracellular pathogen. It enters the body through the gastrointestinal tract after ingestion of contaminated food. In the early and mid 1980's large outbreaks of L.monocytogenes occurred in both pregnant women and people who where immunocompromised.
The first outbreak that demonstrated indirect transmission from an animal reservoir was reported from the Atlantic maritime provinces of Canada, in this outbreak L.monocytogenes contaminated sheep manure used to fertilize cabbages, which where placed in cold storage over the winter.
Active surveillance in the USA suggests an annual incidence of 0.7 cases per 1000,000 approximately 1700 cases of listerosis occur annually in the USA with a mortality rate of 40%.
Two-thirds of cases of listerosis in adults occur in people who have immunocompromised immunity. L.monocytogenes is mainly cell-mediated via TH1 cells. Individuals having
weaker cellular immunity including the elderly, neonates, patients undergoing immunosuppressive drug treatment or those who have immunosuppressive diseases such
As AIDS, have increased susceptibility to listerosis. Alcoholism, diabetes mellitus, and cirrhosis also contribute to the risk of infection.
Acute listerosis is quite rare. The acute disease is usually characterized by bacteriama and meningitis and has a mortality rate of approximately 20%. Although there are about 2500 cases of acute listerosis each year, about 500 cases e
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