Summary of Awards to Date

Contribution of phyllosphere microbiota to the persistence of Escherichia coli O157:H7 ATCC 700728 on field-grown lettuce.


Apr. 1, 2009 - Mar. 31, 2010

Award Number


Amount Awarded



Maria Marco, Ph.D
University of California, Davis


L. Harris


Plant surfaces (also known as the phyllosphere) are colonized by indigenous communities of microorganisms (here termed microbiota). The composition of the phyllosphere microbiota can differ depending on environmental factors including the time of year and moisture levels. Harris et ai (unpublished) found in previous California Lettuce Research Board (CLRB)-funded projects that these environmental factors might also influence the persistence of E. coli O157:H7 on Romaine lettuce plants in the field. However, a current gap in our knowledge is whether the indigenous phyllosphere microbiota also contributes to E. coli O157:H7 persistence. We propose to identify the bacterial communities present in the phyllosphere of overhead and drip irrigated Romaine lettuce prior to and following inoculation with attenuated E. coli O157:H7. Bacterial diversity will be assessed using culture-independent methods with high-density 16S rRNA phylogenetic DNA microarrays. The culturable fraction of bacteria will also be quantified on laboratory culture media. Bacterial plant isolates with the ability to inhibit the growth of E. coli O157:H7 will be identified. The project will provide much needed information aimed at reducing the risk of E. coli O157:H7 survival on leafy greens.