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We hypothesize that vertebrate populations (especially cattle and wild birds) function as a key source of E. coli O157:H7 (EcO157) contamination of watersheds where leafy greens and other leafy vegetables are grown; that climate, landscape attributes, and irrigation practices correlate with increased risks of EcO157 and commensal E. coli contamination; and in-field contamination of leafy greens plants with EcO157 relates to combinations of production practices and environmental risk factors in the Central California Coast, specifically, the San Juan Valley region. The major objectives of this grant to UC Davis are to collaborate with, and assist, ARS in (1) quantifying environmental loading by vertebrate sources, especially feral swine, (2) characterizing the predisposing conditions for hydrological transport of EcO157 and E. coli to leafy green fields, (3) identifying the in-field mechanism(s) of contamination of leafy greens, and (4) developing and disseminating educational materials for growers of fresh produce and the livestock community about microbial water quality, potential impacts on down-stream stakeholders, and effective BMPs for improving water quality.
Approach:
To conduct an in-depth longitudinal study that identifies the key biotic and abiotic processes that sufficiently load, then hydrologically link and disseminate, primary environmental reservoirs of EcO157 within and between leafy greens fields, resulting in bacterial contamination of this raw agricultural commodity. For each node (vertebrate sources, water, soil, leafy greens) of the system, the cooperator will collect a detailed set of covariates that will be used to identify critical control points, points of environmental amplification, and management practices that either elevate or decrease the risk of in-field contamination and dissemination of EcO157 on leafy greens. Samples collected, will be analyzed by the ARS lab for presence of EcO157 and strains isolated will be genotyped by Multi-Locus Variable number tandem repeat Analysis (MLVA) and Pulsed Field Gel Electrophorsis (PFGE) for purposes of source-tracking information, and thus, pinpointing the mechanisms that link and disseminate vertebrate sources of EcO157 within and between fields of leafy greens.