Summary of Awards to Date

Influence of moisture and phyllosphere microbiota on the persistence of E. coli O157:H7 on lettuce plants.

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Feb. 1, 2010 - Jan. 31, 2012

Award Number


Funding Agency

Center for Produce Safety

Amount Awarded



Maria Marco, Ph.D
University of California, Davis


Harris, L.


Fresh fruits and vegetables have been increasingly implicated in outbreaks of foodborne illness, and in particular, outbreaks of enterohemorrhagic Escherichia coli O157:H7 have been associated with consumption of leafy green vegetables. Lettuce is the main item within this group responsible for produce-associated outbreaks and pathogen contamination of the lettuce plants likely occurred in the field prior to harvest. This project will investigate biotic (microbial) and abiotic factors which might affect persistence levels of E. coli O157:H7 on field-grown lettuce. Specifically, the indigenous microorganisms (collectively termed microbiota) residing on the leaf surfaces, or phyllosphere, of lettuce plants will be identified using high-throughput culture-independent approaches. Field-grown lettuce with and without prior exposure to an attenuated (non-pathogenic) E. coli O157:H7 strain will be examined to identify members of the indigenous microbiota positively or negatively correlated with the persistence of this strain in the field. Environmental conditions, and in particular extremes and fluctuations in moisture and temperature on plants, will also be investigated in growth chamber experiments designed to measure the contributions of these factors to E. coli persistence. This project will advance knowledge of the factors affecting E. coli O157:H7 survival on lettuce which can be applied to the development of improved control measures aimed at mitigating the risk of the organism surviving after a contamination event.