E. coli in spotlight during Monterey Conference

MARIE VASARI - MediaNews

Article Launched: 09/12/2008 01:33:35 AM PDT


Source of Article:  http://www.mercurynews.com/centralcoast/ci_10445172

A tiny microbe with a larger-than-life personality, Escherichia coli O157:H7 can't be seen with the naked eye.

But its impact -- and its long shadow over the Salinas Valley's produce industry -- were unmistakable Thursday during a daylong research conference in Monterey. The event brought together researchers, growers, retailers and food safety experts to introduce the results of a $2 million research project funded by Fresh Express.

In a conference that raised as many questions as it did answers, one thing was made clear by the nine research projects presented: E. coli O157:H7 is nothing if not sticky, sneaky and stubborn.

The pathogen, the culprit behind a nationwide recall of spinach two years ago, remains largely an unknown entity to researchers. Exactly how it hides on its host, just how it is spread, and what if anything speeds or stops its dissemination through the food production cycle are questions that scientists and the agricultural industry have been challenged to answer.

There's little question that mass production methods commonly used in the bagged salad industry exacerbate the problem, as huge volumes of cut leafy greens are mixed together in rinse solutions, then either shaken or spun dry. Even tiny amounts of pathogens can be spread throughout large lots of product.

But event moderator Michael Osterholm, executive director of the University of Minnesota Center for Infectious Disease Research and Policy, and an advisor to Fresh Express, said it's unlikely that the American public is ready to give up the convenience of ready-to-eat leafy greens. He said he is a strong proponent of irradiation as a final step in a series of measures to ensure that fresh-cut produce risks are minimized.

Some of the findings

Among the findings of the conference:

Jorge Girón, assistant professor in the department of immunobiology, University of Arizona, led a team that demonstrated the pathogen might somehow interact biologically with the plant in order to colonize it. Under lab conditions, his team was able to show stoma -- a pore in the epidermis of a leaf -- opening in response to an E. coli presence, creating a safe haven on a spinach leaf where the pathogen crawls inside for food and shelter. Just how the E. coli manipulates the stoma remains unknown, he said.

Ozone -- either in a gas form or in a water solution -- was raised by both Giron and another research team as a more viable option than chlorine for removing the pathogen.

But the research seemed to raise a red flag when it came to the risks of manure-based compost in agricultural uses. A research team led by Xiuping Jiang, associate professor in the department of food science and human nutrition at Clemson University, tested various composts to demonstrate pathogen regrowth in compost that has been heat-treated, and E. coli, salmonella and listeria pathogens showed abilities to survive on the surface of compost heaps even when internal temperatures were sufficient to kill organisms.

Problems in the field

The research studies have implications for some of the most commonly used processes.

A common tool used in the field to cut and core heads of lettuce was called into question by a study headed by Michael Doyle, professor of food microbiology and director of the Center for Food Safety, University of Georgia. Doyle and his team found that a flat blade contaminated by soil containing E. coli and then used on lettuce heads could transfer the pathogen to 10 consecutively processed heads, and chlorine had only limited effectiveness against the pathogen.

He said the findings could challenge the industry to re-examine its practice of coring lettuce in the field, as opposed to in a processing plant, as it used to do.

Some varieties of spinach could prove more resistant to E. coli just by their inherent structure. Jacqueline Fletcher, professor of plant pathology at Oklahoma State University and director of the National Institute for Microbial Forensics and Food and Agricultural Biosecurity, led a team whose research suggests that some varieties, like the lumpy-surfaced Bordeaux, might hold the pathogen in surface crevices more than smoother varieties.

But it was her team's research into insects that raised even bigger issues.

Insects a problem

Sampling insect populations in spinach fields in San Ardo and Hollister, her team found significant fly populations, including some which were E. coli O157:H7 positive. Flies exposed to inoculated manure can transfer the pathogen to the surface of a spinach leaf, but Fletcher said further research is required before results can be conclusively drawn.

Among the implications she projected from the findings for growers could be more attention to cultivar choices and pest management in the future.

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