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Salmonella With Your Salad?

Home gardeners can harvest bacteria along with tomatoes

FRIDAY, Nov. 2, 2001 (HealthDayNews) -- Home gardeners who use untreated manure on tomato plants could be creating a source for salmonella poisoning, new research shows.

Tomatoes can become contaminated by salmonella even when the exposure occurs before the plant starts to bear fruit, the study says.

Salmonella, food-borne bacteria that causes gastrointestinal illness in people, is found in the intestinal tracts of animals. Symptoms, which include fever, chills, abdominal cramps and diarrhea, usually appear 12 to 72 hours after infection and last four to seven days. Most people recover without treatment, but diarrhea can be severe enough to require hospitalization, according to the Centers for Disease Control and Prevention.

Each year, 40,000 cases of salmonella poisoning are reported in the United States, but many more mild cases are not reported, the CDC says.

One way the bacteria get transferred from animals to people, experts say, is through the use of raw manure as fertilizer. Commercial growers are prohibited from using raw manure on crops, but family farmers and home gardeners sometimes use untreated manure, which often is available free.

Because tomatoes have been traced as the source of several salmonella outbreaks in recent years, researchers at the University of Georgia and the U.S. Food and Drug Administration decided to investigate the fertilizer as a possible origin, says Larry Beuchat, a professor of food biology at Georgia and lead author of the study.

They inoculated tomato plant stems and flowers, which bloom before the tomatoes appear, with salmonella, Beuchat says, finding that the microorganism survived for 49 days on the surface of the tomato and possibly even invaded the pulp.

Almost 40 percent of the tomatoes harvested from plants that had been exposed to salmonella -- either on the stem or the flower -- also were contaminated with the bacteria, the study says. Of the salmonella-contaminated tomatoes, 82 percent had the bacteria on the surface, and 55 percent had salmonella in the pulp.

"Tomato stems and flowers are possible sites at which salmonella may attach and remain viable during fruit development, thus serving as routes or reservoirs for contaminating ripened fruit," Beuchat says. Details appear in the October issue of the journal Applied and Environmental Microbiology.

Michael Pariza, director of the Food Research Institute at the University of Wisconsin, says salmonella is not particularly hardy. It's fairly easy to kill with heat, and it normally does not thrive in acidic environments, as you'd find in a tomato, he says.

"The findings are surprising, but it fits with what we know about the problem with bean sprouts," Pariza says.

Vegetables carry less risk of salmonella contamination than meat, eggs and poultry, but bean sprouts have been sources of occasional outbreaks. Salmonella gets into the sprout as it's developing, Pariza says, and then makes it onto the dinner table.

What To Do

Using manure as fertilizer "really is a very good way to make your plants grow," Beuchat says. But use untreated manure only when the land is fallow, he advises. Do not use it after planting seeds or before the harvest.

And because salmonella can survive for relatively long periods on vegetables, it's a good idea to wash them well before eating them, he says.

To learn more about salmonella and other food-borne infections, visit the CDC online or check out information from the Iowa State University Extension Service.

Or, to find out about other food safety issues, from genetically engineered foods to mad cow disease and more, visit the Center for Food Safety online.

SOURCES: Interviews with Larry Beuchat, Ph.D., professor of food biology, College of Agricultural and Environmental Sciences, University of Georgia, Griffin, Ga.; Michael Pariza, director, Food Research Institute, University of Wisconsin, Madison. Wis.; October 2001 Applied and Environmental Microbiology
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