Summary of Awards to Date

Survival of E. coli on soil amendments and irrigation water in leafy green field environments.


Oct. 1, 2009 - Sep. 30, 2010

Award Number


Amount Awarded



Steven Koike
University of California Cooperative Extension, Monterey County


Michael Cahn, Ph.D.


Fresh market leafy green vegetables periodically are subject to contamination from foodborne human pathogens such as E. coli. Field aspects of such contamination are not well understood, and there is a lack of information on where and how E. coli comes in contact with leafy greens in the field, how E. coli survives there, and how production factors influence this pathogen. It is notable that few in-field projects have been conducted to address such issues as they pertain to commercial environments for leafy greens in California. Our plan is to continue to develop field-generated information on the survival of E. coli under actual production environments for coastal California leafy greens. We will validate our initial findings regarding survival of generic and non-toxigenic O157:H7 strains of E. coli when introduced to irrigation water, soil, and plants of a spinach field. With this simulation of a contamination event in spinach, we document survival of E. coli under field conditions; such information will be useful in further improving metrics and regulatory measures. We will evaluate survival of generic and non-toxigenic O157:H7 strains when introduced as contaminants in fertilizer inputs (compost, amendments, teas or other extracts) that are subject to soil cultivation and other practices.

Technical Abstract

Fresh market leafy green vegetables are periodically contaminated with foodborne human pathogens such as E. coli. However, there is little documented information about the ecology and survival of E. coli in production settings. Laboratory, growth chamber, and greenhouse studies provide some information on how E. coli and other pathogens might interact with leafy vegetables such as lettuce and spinach. It is notable, though, that few in-field research projects have been used to address such issues. In our proposal, we will further validate and confirm how both generic and attenuated,
non-toxigenic O157:H7 strains of E. coli survive when introduced to soil, water, and plants in a spinach production field. In a replicated field trial we will inoculate soil with both E. coli strains, grow a spinach crop in this field, and then monitor survival by sampling and testing soil, water runoff, and spinach plants. In another experiment, we will inoculate mature spinach plants, incorporate such plants into the field by disking, and test soil for E. coli survival. This information should contribute to our understanding of how E. coli actually functions in a commercial production setting. We will examine how generic and non-toxigenic O157:H7 strains of E. coli survive when introduced into field settings via production inputs. We will inoculate fertilizer and amendment materials such as compost, organic fertilizers, and compost teas. We will incorporate materials into the soil and then test soil for survival of the inoculated strains following soil cultivation. We will also grow a lettuce crop in these plots and evaluate plants for any indications of contamination. A strength of our research team is our familiarity with and expertise in field production aspects of leafy vegetable in coastal California. Our roles as field researchers and educators provide us with strong industry connections, and our project will therefore have a prominent extension component as we work directly with growers and other industry personnel.