ORLANDO, Fla. — In the fight to keep produce free of contamination, it’s sometimes forgotten that plants such as leafy greens grow in nature and have bacteria on them all the time.
One project funded by the Davis, Calif.-based Center for Produce Safety examines how bacteria on lettuce leaves can actually protect the plant from harmful pathogens.
Johan Leveau, assistant professor of plant pathology at the University of California-Davis, presented his study seeking to identify “indexing species” that could become contamination indicators during the June 28 Produce Research Symposium in Orlando, Fla.
“Index organisms have predictive value,” Leveau said. “You can go out in a field, look at a field and sample it. You can come up with some prediction of how susceptible it would be if E. coli contamination were to take place and what would be the probability of E. coli persisting in that field.”
In a two-year study, Leveau tested 176 samples, but he never came across the E. coli O15:H7 strain. Although the study failed to correlate the presence of E. coli and the native microbiota on plants, he said it would be useful for scientists use E. coli samples to examine what kind of bacterial community could be associated with the samples.
Bob Whitaker, chief science and technology officer for the Produce Marketing Association, Washington, D.C., said the indexing species could tell scientists conditions that could support pathogens. That, he said, might trigger a grower to test his field for contamination five to 10 times more rigorously than normal because the conditions might support pathogen growth.
“The whole thing was to look at the dynamic between naturally occurring organisms and invading pathogens,” Whitaker said. “We know there are bacteria that do not coexist well with E. coli and salmonella. These antagonists kill them.
“Johan’s work goes both ways,” he said. “If we could identify presence of bacteria that could kill, we would feel better and have a different set of risks to manage. It’s interesting work.”
Leveau said it’s difficult for scientists to predict when E. coli can contaminate lettuce, because those events are rare and don’t strike all areas of a field.
He said testing for such indicator species provide a broader view of what’s on plant surfaces. Leveau said he expects testing methodology to become less expensive and provide faster results, with technology advances allowing in-field testing.
Ed Beckman, president of California Tomato Farmers, Fresno, said growers should view this information as another tool.
“If we go back to growers, they would ask if it’s another test,” he said. “This is beyond that. It’s taking a much deeper look and helping us answer some questions. It’s providing us a bit of an exact answer.
“It’s not unlike some of the other forecasting models we have used in production agriculture to deal with the diseases out there,” Beckman said. “If it’s portrayed in that light, I think the buy-in from the industry could be quite a bit stronger.”
Information on the center’s research is on its website.