The complex and poorly researched E. coli O157:H7 issue, although mostly a threat in leafy vegetables, should be a concern for the California wine grape industry also, says a Monterey County farm advisor.
Steve Koike, who specializes in plant pathology, closely monitors E. coli in vegetables, and he recently warned Monterey County grape growers at a seminar in Salinas that wildlife vectors of the disease could possibly be linked to their vineyards.
The habitat of vineyards and the grapes themselves are attractive to wildlife. “That means,” he said, “that if wild animals carrying E. coli were present they could possibly drop it in your fields. I'm not saying that does happen, but research down the road will have to resolve the question.”
Given the current “hot, tense, and problematic” nature of the E. coli issue, some people, he said, are looking for places to blame as sources of the pathogen.
For example, if E. coli were found in a lettuce field downslope from a vineyard, the vineyard might be suspect as the potential source of bacteria carried by runoff into crops.
As a defense in such a case, the grape grower would need to be able to identify which strain of the disease, if any, was present on his fields to know whether it was the same as that in the lettuce.
Produce growers, Koike explained, are under tremendous pressure from buyers and distributors to install fences to exclude larger wildlife, do testing, and take other expensive steps to provide safe food for consumers.
Meanwhile, a host of responses ranging from self-regulation by growers to deep involvement by regulatory agencies and interest groups is heightening the tension.
Adding to the controversy is the fact that E. coli has many strains, some harmful, some benign, and sophisticated tests are needed to distinguish them.
“We all want to make lettuce, spinach, and other vegetables safe for consumers, but the biological fact is these crops are grown out-of-doors and exposed to E. coli, whether it is harmful or not harmful. But until we have more research-based information, we really don't know how to give that protection,” Koike said.
His advice to grape growers is to realize the complexities of E. coli and be aware of its many forms. “When you read a newspaper article about a study, be critical about the source of it. Conclusions need to be based on sound research, and hopefully we will in time be able to do that.”
Particularly lacking, he said, is research on how the various strains of E. coli, which has the rare ability to reside in both animals and plants, operate in both natural settings and cultivated agriculture.
Along with the need for more sound science, Koike said, communication about the issue needs to be improved. He recalled that after the E. coli incident in spinach in the fall of 2006, governmental agencies initially gave out misleading or incomplete information.
One example: when the source of contamination was found to be in San Benito County, the area was not immediately specified, and Monterey County and the Salinas Valley were implicated.
Koike also said research agencies, such as USDA and the University of California, particularly when animal, plant, and water and soil specialties are all involved, have not necessarily communicated closely with each other.
Before the E. coli issue, it was not likely that livestock specialists would collaborate with plant pathologists. Efforts are being made, however, to improve the exchange of information between researchers and agricultural industries at local, state, and federal levels.
Koike said key elements of the mystery confronting researchers include the actual source of E. coli, how it survives, why it tends to emerge in late summer, and how it spreads.
Attempts in the popular media to apply results of any available research to the problem have been misleading, he said. One publicized theory is that the pathogen is taken up by the affected crop. Koike said that notion comes from studies done in growth chambers or greenhouses, with plants grown in non-mineral soils, not typical soils found in coastal California. Plants in the studies were exposed to “astronomically high levels” of the pathogen.
“Yes, in this setting there was some internalization of E. coli,” he said, “but what's important to tell the media and the consumer is that this was a very artificial setting with very high levels of inoculum and nothing that resembled a field situation.”
Unfortunately, the researcher in this study, although he acknowledged the artificial setting of the trials, did link a health threat with consumption of fresh produce, Koike said.
Moreover, Koike added, years of practical, field research in the Salinas Valley have never found any connection between E. coli and internalization in plants. Still, he said, plant pathologists and others will continue to investigate the matter.
Another question is whether E. coli is spread by flooding water and if so how long it persists and how far it goes. “I can tell you right now we don't have answers, but we believe any information should be based on field research” he said, adding that his three-year survey, with extensive testing and analyses, failed to find E. coli O157 in soil, water, creek sediment, or plant samples.
However, USDA researchers, he said, later found one sample in one year in the same geographical area. “So that brings up the question about sampling and detection sensitivity. These are questions we have to answer.”
Misconceptions have emerged about E. coli being on lettuce or spinach seed, based on some findings with alfalfa seed used for sprouts. Koike said there have been rare instances of E. coli and salmonella being found on alfalfa sprouts produced in moist, growth chamber environments.
But he said there is no evidence the pathogens occur on vegetable seed and if they did, planting the seed outdoors in mineral soils would leave little likelihood of the pathogens surviving competition from other microflora in the soil.
The exact role of wildlife as potential vectors of the pathogens is not clear. Wild pigs were linked to the San Benito County spinach case, but commercial cattle also are known sources of E. coli. Fences around vegetable fields were proposed as a solution.
“We don't have enough research-based information now to justify erection of fences. And fences might keep out some animals but not others, such as rodents or birds, that might also be found to be vectors,” Koike said.