Wash-Resistant Bacteria Taint Foods
by J. Raloff
and the Food and Drug Administrationhave long advocated washing fresh fruits and vegetables to evict any germs they harbor. However, it takes more than simple washing to eliminate all of the bacteria, new studies find.
Foodborne microbes trigger some 81 million cases of disease in the United States each year, according to the General Accounting Office (GAO), an investigative arm of Congress. Moms
Elizabeth Ehrenfeld of IDEXX Labs, a diagnostic testing service in Westbrook, Maine, examined 39 samples of fresh bean sprouts, all purchased from local grocers. On average, each gram of sprouts hosted more than 10 million coliform bacteria, she reported last week at an American Society for Microbiology meeting in Atlanta. Though not usually posing a disease risk themselves, these bacteria, also present in soil, point to the potential for coincident contamination of crops with pathogens that might be present in fresh manure or human feces. Both are common crop fertilizers throughout much of the world.
Moreover, Ehrenfeld found that 10 samples of the fresh sprouts harbored E. coli--some with around 7,000 of the bacteria per gram. The presence of such fecal bacteria indicates that the samples were tainted by dirty hands during harvesting or distribution, she says.
"The surprise for me," she told Science News, "was that washing the sprouts did not drop the bacterial counts very much." After depositing up to 100 million E. coli or Salmonella on bacteriafree sprouts, she washed them three times in clean water. While this reduced the bacterial population, it still left up to 1 million microbes per gram of food--many thousands of times the number needed to sicken someone with a weakened immune system.
At the meeting, John Lopes of Microcide in Troy, Mich., reported finding an average of 63,000 Listeria and Aeromonas bacteria per gram of cauliflower from local groceries and 16 million per gram of radish. The bacteria detected do not cause human disease, but their presence shows that these foods can harbor live bacteria encountered in food handlingincluding deadly forms of Listeria.
Contributing to the problem of tainted foods, an April 30 GAO report argues, is the increasing share of U.S. produce coming from countries without strict laws governing hygiene in food production and handling. Though federal law bans the importation of meat from nations without food safety systems equivalent to those in the United States, no similar prohibition exists for other foods.
Lacking resources to inspect even 2 percent of nonmeat imports, FDA cannot be relied upon to keep pathogen-tainted products out of the U.S. food supply, the GAO report concludes.
Taken together, these data are fueling the development of antimicrobial agents safe enough for kitchen use on foods.
Susan S. Sumner of Virginia Polytechnic Institute in Blacksburg finds that washing tainted produce with water "is better than doing nothing--but not a whole lot better." Later this year, however, she and graduate student Jim Wright plan to report that they can infect apples with a deadly strain of E. coli at a concentration of 10,000 bacteria per gram, then eliminate them all by dipping the fruit in a nontoxic mix of vinegar and off-the-shelf hydrogen peroxide. This E. coli, known as O157:H7, has been implicated in the deaths of people who consumed tainted cider or hamburgers.
This week, Ecolab of Saint Paul, Minn., announced it had received approval from the Environmental Protection Agency to market a patented version of the disinfectant combo to food distributors for treating fresh vegetables, including mushrooms, lettuce, onions, and bell peppers.
Lopes says his company has EPA approval but is awaiting FDA approval of another chlorinefree, antibacterial product for kitchen use. "You just dissolve it in tap water, spray it on foods, and kill the germs," he says.
From Science News, Vol. 153, No. 22, May 30, 1998,
Copyright Ó 1998 by Science Service.
Lopes, J.A., A. Rillo, and R.J. Lopes. 1998. Effect of storage temperature on population density of natural and pathogenic bacteria on vegetables. Meeting of the American Society for Microbiology Abstract P-107. May. Atlanta.
Potter, A.P., and E.E. Ehrenfeld. 1998. Microbial loads of bean sprouts: Coloform, E. coli, and salmonella. Meeting of the American Society for Microbiology Abstract Q-243. May. Atlanta.
U.S. General Accounting Office. 1998. Federal efforts to ensure the safety of imported food are inconsistent and unreliable. Report GAO/RCED 98-103.
1997. Outbreaks of Escherichia coli O157:H7 infection and cryptosporidiosis associated with drinking unpasteurized apple ciderConnecticut and New York, October 1996. Morbidity and Mortality Weekly Report 46(Jan. 10):4.
Peters, D., S.S. Sumner, et al. 1996. Control of pathogenic bacteria on fresh produce. Meeting of the International Association of Milk, Food and Environmental Sanitarians Abstract 168. July. Seattle.
Raloff, J. 1996. How to disinfect your salad. Science News Online. Sept. 28.
______. 1996. Sponges and sinks and rags, oh my! Science News 150(Sept. 14):172.
______. 1996. Tracking and tackling foodborne germs. Science News 149(May 25):326.
Richert, R., J. Albrecht, S.S. Sumner, et al. 1995. Survival and growth of E. coli O157:H7 on produce. Journal of Food Protection 58(Supplement):19.
Wilson, D. 1998. Food poisonings phony figure. Columbia Journalism Review (May/June):16.
American Society for Microbiology
1325 Massachusetts Avenue, N.W.
Washington, DC 20005-4171
Web site: http://www.asmusa.org
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Saint Paul, MN 55102
Web site: http://www.ecolab.com
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Westbrook, ME 04092
2209 Niagara Drive
Troy, MI 48083-5933
Web site: http://www.microcideinc.com
Susan S. Sumner
Virginia Polytechnic Institute and State University
College of Agriculture and Life Sciences
Department of Food Science and Technology
Blacksburg, VA 24061-0418
copyright 1998 ScienceService