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Testing for deadly bacteria.

Most food poisoning is unpleasant, but some types are life-threatening. Consumption of food contaminated with the bacteria Listeria monocytogenes can cause a fatal illness--listeriosis. In the U.S., there are 1,850 cases and 460 deaths per year.

Consumption of certain foods is linked to increased risk for listeriosis. Soft cheeses and deli meats top the list, though Listeria can be found in almost all food types. The organism present in soil and groundwater can find its way onto vegetation eaten by animals. Even healthy creatures can carry Listeria in their intestinal tracts, as part of the bacterial microflora. Its ubiquitous nature makes introduction into food processing environments routine, making detection and control vital.

Although healthy people are relatively resistant to Listeria, infection frequently is fatal to the very old, anyone who is immunocompromised, and fetuses. As the mean age of the population rises and immunocompromising diseases such as cancer and AIDS increase in frequency, there is a rise in the number of people at risk.

Testing for Listeria usually involves sampling foods and monitoring the food processing environment. Such testing provides a check on the efficiency of cleaning operations and can pinpoint locations requiring extra attention before bacteria become established and multiply.

The need to obtain results quickly has resulted in the introduction of new formats, called rapid tests, most of which are based on enrichment. The food sample is mixed with bacterial culture medium containing selective agents and incubated for 24-48 hours. The bacteria present after enrichment are characterized, some through rapid tests using antibodies. Ideally, the antibodies recognize Listeria, but not other bacteria. Another format uses a nucleic acid probe specific to Listeria to identify any of those organisms present after enrichment by using chemicals that become colored only in the presence of the bacteria. One test is available that omits enrichment, making it possible to confirm within 24 hours that Listeria are present. Within an additional 24 hours, it is possible to determine whether the detected Listeria are pathogenic (can make a person sick) or not.
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Title Annotation:food poisoning
Publication:USA Today (Magazine)
Date:Feb 1, 1993
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