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Lethal Listeria surfaces on fresh vegetables.

Lethal Listeria surfaces on fresh vegetables

In a survey of 10 types of fresh produce, scientists have uncovered potentially deadly Listeria monocytogenes bacteria in samples of cabbage, cucumbers, potatoes and radishes. Only a small percentage of the cabbages and cucumbers harbored the bacteria -- the only Listeria species known to cause illness and death in humans -- but about 26 percent of the potatoes and 30 percent of the radishes were contaminated. The researchers found no L. monocytogenes in broccoli, carrots, cauliflower, lettuce, mushrooms or tomatoes, says study leader Judy E. Heisick of the FDA's Center for Microbiological Investigation in Minneapolis.

The study, in which Heisick and her co-workers tested 1,000 vegetable samples obtained from two Minneapolis supermarkets, represents the most extensive work to date documenting the organism's presence on fresh produce, says Robert E. Brackett, a food microbiologist at the University of Georgia Agricultural Experiment Station in Griffin.

Systematic searches in the past have failed to detect the organism on large numbers of produce samples. However, researchers have proved it the perpetrator in at least two epidemics of food-borne illness and death. In 1985, scientists found it in a type of soft cheese that caused human deaths and stillbirths in southern California. And in 1981, researchers linked L. monocytogenes in coleslaw to a cluster of Canadian deaths, Heisick says.

In most healthy adults, the bacteria cause no symptoms or, at worst, a flu-like illness. But in fetuses, newborns and people with depressed immune systems, such as chemotherapy patients and some elderly individuals, the organism can enter the brain, leading to meningitis and often to death, says Sita R. Tatini of the University of Minnesota at Minneapolis-St. Paul. The brain infection, called listeriosis, afflicts an estimated 1,600 people annually in the United States, killing about 400, Heisick says.

Scientists do not know what levels of the bacteria are required to cause literiosis in humans, and Heisick says she did not calculate the levels in her samples because no reliable methods exist for such calculations.

To reduce contamination, she recommends thoroughly scrubbing fresh vegetables, which may bear bacteria-harboring dirt on their surfaces or within pores or cracks. However, she and her co-workers write in the August APPLIED AND ENVIRONMENTAL MICROBIOLOGY, "it is not known what, if any, degree of cleaning would eliminate contamination of fresh produce by L. monocytogenes."
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Title Annotation:bacteria
Author:Wickelgren, I.
Publication:Science News
Date:Aug 19, 1989
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