FDA studies bacteria that could fight salmonella in tomatoes

Salmonella is a particular problem for tomato growers in Florida, Georgia, Virginia and other states along the East Coast. And the tomato industry is eager for a way to reduce salmonella contamination and regain consumer confidence, said Reggie Brown of the Florida Tomato Exchange. An outbreak of salmonella illness last year was incorrectly linked to tomatoes -- later traced to jalapeño peppers from Mexico -- but not before the tomato industry suffered losses of about $150 million. Consumer demand still has not returned to levels before that outbreak, said Reggie Brown, who is not related to Eric Brown.

"Every time someone reports in a news article on food safety about an outbreak associated with salmonella, the word 'tomato' will appear out there," Reggie Brown said. "There's concern and distrust."

The notion of using benign bugs to fight dangerous bugs can be traced to 1917 when microbiologist Felix D'Herelle discovered bacteriophages -- viruses that live within bacteria and can kill other bacteria, said Scott Polodsky, a doctor and science historian who teaches at Harvard Medical School. D'Herelle used phages to successfully treat cholera patients in India; his work caught on in Western Europe.

In recent years, probiotics -- live bacteria that can improve the balance among 400 different types of bacteria that live in the human gastrointestinal system -- have gained a foothold in the United States, appearing in yogurt, milk and other foods. Pre-biotics, which are nutrients that feed beneficial bacteria in humans, are also growing in popularity. Analysts say the global market for probiotic and prebiotic foods reached $15 billion last year, a 13 percent increase over 2007.

Like Brown, other researchers have been trying to find a naturally occurring bacteria that can kill pathogens on human food. Scientists at the U.S. Department of Agriculture reported in 2007 that they isolated microorganisms from baby carrots that suppressed the growth of four harmful pathogens. Last year, the same team applied "good" bacteria to kill salmonella on sprouts.

'Team Tomato'

Brown and his colleagues, known around the FDA as "Team Tomato," made repeated trips to tomato-growing regions on Virginia's Eastern Shore this spring and summer, where they stomped through fields and swamps and collected more than 200 samples from plants, water and soil. Each trip, they stayed with their coolers of water and muck and plants in the same hotel. "I had to leave a substantial tip to satisfy my conscience," Brown said.

Back in their College Park laboratory, Brown and his main collaborator, Alex Enurah, identified more than 300 species before isolating five "good" bacteria.

The "good" bacteria don't appear to be harmful to humans but further investigation is needed, Brown and Enurah said. They intend to test the bacteria on tomatoes grown in research hothouses in the coming months. And they are testing whether the "good" bacteria could prevent salmonella contamination as well as treat fruit that is already tainted. Brown envisions a day when "good" bacteria could be sprayed onto fields of tomatoes just before harvest.

Still, what works in the laboratory often runs into trouble on the farm and never makes it to the grocery store, said Jeri Barak, an assistant professor of plant pathology at the University of Wisconsin at Madison.

"The tripping point for biocontrol has always been commercial application," she said, noting that outside the lab, the process is complicated by the presence of many other bacteria and fungi, and even sunlight. "A lot of times what looks really, really good in the laboratory doesn't work in the field."