THURSDAY, April 10 (HealthDay News) -- Washing fresh fruits and vegetables can reduce the risk of food poisoning, but only irradiation kills almost all disease-causing bacteria, new research shows.

The study suggests that irradiation, which is currently being reviewed by the U.S. Food and Drug Administration, can kill bacteria that are beyond the reach of conventional chemical sanitizers, including inside the leaves of spinach and lettuce.

"If you have pathogens that are inside a leaf, then normal chemical sanitizers are not going to be able to kill those very effectively," said lead researcher Brendan A. Niemira, a microbiologist with the United States Department of Agriculture at the Agricultural Research Service in Wyndmoor, Pa.

"What I have demonstrated is that pathogens that are inside a leaf are killed by radiation," Niemira said. "This is something that has not been demonstrated before."

"The spinach outbreak in the fall of 2006, in particular, raised questions about how these organisms survived the various treatments that are applied -- the rinses and the washes and things, Niemira noted in a statement.

In addition, Niemira looked at pathogens that are protected inside a biofilm. Pathogens form complex communities on the surfaces of leaves called biofilms, he explained. "Once they are inside these biofilms, they are very difficult to kill."

In irradiation, food is exposed to electronic beams that create positive and negative charges. This process disrupts cell-destroying pathogens such as E. coli and salmonella, as well as insects.

Irradiation is used to kill bacteria and insects to extend the shelf life of food, for example, by delaying the ripening of fruits or the sprouting of vegetables. Irradiated foods, except for spices, must be labeled as such, according to the FDA. The FDA has been considering whether to approve irradiation to prevent the spread of harmful bacteria since 1999, Niemira noted.

The USDA researchers presented their findings Thursday at the American Chemical Society annual meeting, in New Orleans.

In their study, Niemira and his colleagues found a way to draw bacteria into the leaves of leafy green vegetables. The vegetables were then treated either with a three-minute water bath, three minutes of chemical treatment, or irradiation.

The researchers found that washing with plain water did not reduce bacteria levels in spinach or lettuce. Chemical treatment did not significantly reduce E. coli in spinach leaves and was less than 90 percent effective when it came to removing E. coli from lettuce.

Irradiation, however, reduced the level of E. coli by 99.99 percent in lettuce and by 99.9 percent in spinach, the researchers found.

In tests of biofilms that contained salmonella or E. coli, those that contained salmonella died more easily when exposed to radiation, while E. coli was a little bit more resistant, Niemira noted.

Irradiation has been criticized as a stopgap measure that ignores the bigger problem of how food in the United States is grown, processed and sold. Critics also claim that irradiation changes the taste and nutritional value of food, in addition to producing toxic chemicals.

"We have concerns about food irradiation," said Joseph Mendelson III, legal director of the Center for Food Safety. "We think food irradiation is basically a Band-Aid approach to dealing with how you produce food and how you process it."

In addition, Mendelson is concerned about the process itself. "We know that irradiation produces unique substances in food that may have toxic effects. We also know that it affects both the nutritional quality of food and characteristics of the food that make it a pleasure to eat," he said.

"We don't think it's a viable technology. We think it's something consumers should avoid," Mendelson said.

However, supporters of irradiation say that the process is the only practical way to prevent spread of dangerous bacteria and increase shelf life, given the realities of how food is produced today.

"When you consider that the global problem with food will only increase, we need to preserve as much food as possible for distribution as we increase our population," said Dr. Philip Tierno, director of clinical microbiology and immunology at New York University Medical Center.

"I think irradiation is a very good alternative technique, and it should be used more than it is," Tierno said. "Irradiated food products may be the means for extending shelf life of foods and, in addition, the killing of potential pathogens -- it may be the only means -- there may be no alternative," he said.

Niemira noted that scientific evidence shows that irradiation is safe and nutritional values remain unchanged.

"All the researchers showed that irradiated food is perfectly safe," Niemira said. "Do people want to approach the subject of irradiated food from a straight scientific standpoint -- as safe and effective? If there are other issues they want to bring to that and from a philosophical perspective, they say they don't want to eat irradiated food, well, that's another issue."

More information

For more about irradiated food, visit the U.S. Food and Drug Administration.

SOURCES: Brendan A. Niemira, Ph.D., microbiologist, United States Department of Agriculture, Agricultural Research Service, Wyndmoor, Pa.; Philip Tierno, M.D., Ph.D., director, clinical microbiology and immunology, New York University Medical Center, New York City; Joseph Mendelson III, legal director, Center for Food Safety, Washington, D.C.; April 10, 2008, presentation, American Chemical Society annual meeting, New Orleans

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