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article imagePossible Solution to Salmonella Outbreaks in Tomatoes Discovered

By Bob Ewing     Jun 13, 2008 in Food
The answer to preventing future Salmonella outbreaks in tomatoes is fighting microbes with microbes, according to new research by a University of Guelph food science professor.
Keith Warriner is by a University of Guelph food science professor. Warriner, working with graduate student Jianxiong Ye, may have the answer to preventing future Salmonella outbreaks in tomatoes.
Warriner has discovered a method that could effectively eliminate Salmonella contaminations by combining an antagonistic bacterium naturally found on tomatoes with viruses that infect the pathogen and introducing the solution to the plant.
"We have Salmonella outbreaks in tomatoes almost every year, and it's a large food safety risk," said Warriner, who has been studying the issue for the past five years.
"Because Salmonella can become internalized in tomatoes, simply washing cannot inactivate or remove the pathogen. Preventing contamination of the tomato during cultivation and post-harvest is also problematic."
The tomatoes would be treated at the flowering stage.
The researchers began by examining the types of bacteria that naturally exist on tomatoes and found that the microflora profile of the fruit differed depending on whether they were contaminated. Specifically, they discovered that the fruit harbouring Enterobacter prevented Salmonella from establishing.
Mung beans were used because they take only days to grow compared with the months the tomatoes require, he inoculated the beans with Salmonella along with an Enterobacter isolate recovered from tomatoes.
When the Enterobacter strain was co-inoculated with Salmonella it reduced the levels of pathogens on the sprouts but did not eliminate them.
Enterobacter was then combined with a type of virus known as a bacteriophage, which infects bacteria. This combination was successful in eliminating Salmonella from the sprouts.
The next step is to test this combination on tomato flowers.
"We know that if we have Salmonella on the flowers, chances are good that it will contaminate the fruit that develops," said Warriner.
In previous research, he found tomatoes are vulnerable to contamination at the flowering stage. In a study where he exposed tomato flowers to Salmonella, 90 per cent of the harvested fruit was contaminated.
"These tomatoes weren't just contaminated on the surface but in the tissue as well, so washing isn't effective. This is why combating Salmonella contamination is most effective if done at the flowering stage."
The plan is to develop a spray that combines the Enterobacter and bacteriophage that farmers can apply to crops. The solution could also be introduced to the water tomatoes are transported in during the post-harvest stage, effectively cutting off all possible routes of contamination, he said.
"This method addresses the problem at the source rather than coming up with a solution once the tomatoes are contaminated. We hope our biocontrol method will make Salmonella outbreaks linked to tomatoes a thing of the past."
This research was funded by the Ontario Ministry of Agriculture, Food and Rural Affairs food safety research and innovation program and the International Life Sciences Institute North America.
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