Prof Discovers Possible Solution to Salmonella Outbreaks in Tomatoes
June 12, 2008 - News Release
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 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."
His solution is to treat the tomatoes at the flowering stage.
Warriner, along with graduate student Jianxiong Ye, 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.
Using mung beans, which 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.
He then combined Enterobacter 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."
Warriner's goal is to develop a spray combining 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.
Contact
Prof. Keith Warriner
Department of Food Science
519-824-4120, Ext. 56072
kwarrine@uoguelph.ca
For media questions, contact Communications and Public Affairs: Lori Bona Hunt, 519-824-4120, Ext. 53338, or l.hunt@exec.uoguelph.ca, or Deirdre Healey, Ext. 56982 or d.healey@exec.uoguelph.ca.
