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UCCE investigates how E. coli survives in vegetable fields

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The Issue

UCCE investigates how E. coli survives in vegetable fields

E. coli colonies on diagnostic agar medium.

Current evidence from surveys and product testing has shown that California vegetable commodities are rarely contaminated with detectable levels of the human pathogen E. coli O157:H7. However, periodic outbreaks occur. The September 2006 case of E. coli O157:H7 on spinach was a serious example that fundamentally changed the industry and public health landscape regarding food safety measures. To most effectively design risk reduction guidelines and improve food safety management, more information is needed on the biology and ecology of pathogens in actual field production environments. Many studies of E. coli O157:H7 and leafy vegetables are based on laboratory or growth chamber experiments. Many food safety guidelines and policies, by necessity, are based on such studies or on assumptions unrelated to vegetable production. It is imperative that more information be generated from trials involving natural populations of the disease organisms and the microbial-plant-animal ecology as it exists in the field. In addition, we need more information from controlled-inoculation experiments conducted in actual field production settings in California.

What has ANR done?

UC Davis researchers have been studying food-borne pathogens on crops for a number of years. However, because of the heightened concern about E. coli O157:H7 contamination of leafy vegetables, Monterey County farm advisors recently have partnered with food safety specialists Trevor Suslow and Linda Harris of UC Davis to conduct field experiments designed to investigate the ability of E. coli to survive and spread in a production environment. Using various nonpathogenic E. coli isolates as surrogate organisms, they are evaluating how variations in soil moisture and environmental conditions may impact survival in soil, water and on plant surfaces. This team is conducting a series of other experiments to develop information on source-tracking, survival, detection technologies, and field ecology of E. coli.

The Payoff

Field-based scientific data fills in missing information gap

While a thorough examination of food-borne pathogens on leafy green commodities will undoubtedly be a long-term project, University of California researchers have initiated efforts to provide science-based information that can be used to guide industry in food safety policies. For example, it appears likely that soil moisture may significantly influence the persistence of E. coli in the field. These studies are intended to help fill the need for practical, field-oriented studies conducted under actual agricultural production conditions.

Contact

Supporting Unit:

Monterey County, UC ANR Cooperative Extension and UC Davis Department of Plant Science

Steven T. Koike, Mike Cahn, and Richard Smith, UCCE farm advisors, (831) 759-7350, stkoike@ucdavis.edu, mdcahn@ucdavis.edu, rifsmith@ucdavis.edu. Trevor Suslow, (530) 754-8313, tvsuslow@ucdavis.edu, and Linda Harris, (530) 754-9485, ljharris@ucdavis.edu, food safety specialists, UC Davis.