(June 18, 4:07 p.m.) As U.S. health officials continue to search for the source of salmonella that has sickened consumers across the country who ate raw tomatoes, a Canadian researcher may be close to finding the answer for stopping the next outbreak.

Keith Warriner, research scientist in the department of food science at the University of Guelph, Ontario, Canada, claims to have discovered a method to eliminate salmonella by combining a bacterium naturally found on tomatoes with viruses that can prevent the pathogen from establishing itself in the plant.

The most critical time that a tomato plant can be contaminated is during the flowering stage, Warriner said. Therefore, his solution for eliminating the pathogen from tomatoes focuses on that.

“When we put salmonella on these flowers, several weeks later, we not only found salmonella on the surface of the tomato, but in its tissue,” he said.

The significance of this, he said, is once the salmonella is inside the fruit, no amount of washing or sanitizers will kill it.

He said some have suggested using bleach or other sanitizers in the fields on the plants to kill all bacteria.

“The problem there is you kill the flowers and don’t want to kill all bacteria because sometimes we find good bacteria,” he said.

The study

Warriner and a graduate student inoculated tomatoes with salmonella, and when they tested the fruit, some were positive. In those testing negative, researchers found a bacterium called Enterobacter, a nonpathogen naturally present on tomatoes.

“We isolated a lot of Enterobacter from tomatoes and found some strains that were really good at inhibiting salmonella,” he said.

They mixed the Enterobacter with salmonella and using mung bean sprouts – because they germinate faster than tomatoes, shortening the time to study results. They discovered the mixture reduced the amount of salmonella, but did not kill all of it. Then they decided to attack the salmonella from two fronts.

“We had the idea of using bacteriaphage, which are viruses that infect bacteria,” he said.

He said by using a mixture of the Enterobacter and bacteriaphage that infected only salmonella, they were able to eliminate salmonella, while leaving “friendly bacteria” unaffected. “We can selectively kill the salmonella, where a sanitizer will kill everything,” he said.

He said the study proved conclusively that researchers could kill salmonella in mung beans. Now they have to see if it will work on tomatoes. Warriner is confident it will because the Enterobacter they used for the research was isolated from tomatoes, so in theory, it should work.

Field trials began June 16.

“We’re going to start trials on tomato plants by inoculating salmonella into the plants and hopefully prove the same affect,” he said June 13.


Growers and processors will have to wait two to five years for a possible solution to their salmonella woes, though, Warriner said.

“It all depends on who picks it up,” he said. “It’s like anything else — if there is a great demand for it, industry can push things through very quickly. In academia you’re always starved for funding, so things progress fairly slowly.”

Funding thus far has come from the Ontario Ministry of Agriculture, the Food and Rural Affairs’ food safety research and innovation program and the International Life Sciences Institute of North America.

Warriner said he could have a product within two years, but five years looks more probable if an industry player does not step up to the plate to provide funding.

“As an academic you do this research and prove it a success, but really the critical point is do you get a commercial partner willing to invest money to mass-produce and market it and go through the regulatory hurdles,” he said. “We have demonstrated its effectiveness. The commercialization could be a long or short road depending on how people view it.

“I assume there might be some interest, but it’s very difficult to get industry interested because they have to invest a lot of money,” he said. “The actual customers — the farmers and food safety people — have to say they want this product and that’s when things start taking off.”