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SPRING 2009
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Sidebar: Life Sciences

Listeriosis and Listeria

Manifestations of listeriosis include septicemia, meningitis, encephalitis, and intrauterine or cervical infections in pregnant women. The onset time to serious forms of listeriosis range from seven days to two months.

Gastrointestinal symptoms (nausea, vomiting, and diarrhea) may precede more serious forms of listeriosis or may be the only symptoms expressed, and they can begin within 24 hours. Most healthy people show no symptoms. At risk are people who are immunocompromised (by corticosteroids, anticancer drugs, and AIDS); cancer patients (leukemic patients particularly); pregnant women (and the fetus); and the elderly.

The mortality rate for severe invasive listeriosis is 20 percent. An estimated 500 people die each year in the United States from listeriosis.

While most strains of Listeria monocytogenes, a Gram-positive bacterium that is motile by means of flagella, are pathogenic to some degree, recent research by Wiedmann and colleagues as well as others around the world has shown that a considerable proportion of L. monocytogenes show highly reduced ability to cause human disease.

Immuno-gold electronmicroscopy
picture of Listeria monocytogenes,
labeled to detect presence of
internalin A.
 

Immuno-gold electronmicroscopy picture of Listeria monocytogenes, labeled to detect presence of internalin A.

This research may, in the future, facilitate new approaches to focus control strategies on the most virulent Listeria monocytogenes.

The pathogen is found in soil, silage, and other environmental sources, and it is hardy and remarkably resistant to freezing, drying, and salt. L. monocytogenes has been associated with foods such as raw milk, softripened cheeses, ice cream, raw vegetables, and raw and cooked meats and fish.

Adapted from the FDA Center for Food Safety and Applied Nutrition’s Bad Bug Book (http://vm.cfsan.fda.gov)