Summary of Awards to Date

Subsurface contamination and internalization of Escherichia coli O157:H7 in pre-harvest lettuce.

Read Full Publication...


May. 1, 2007 - Oct. 31, 2008

Funding Agency

Fresh Express

Amount Awarded



Michael P. Doyle, Ph.D.
University of Georgia


Beuchat, L., Erickson, M.,Riley, D., Zhang, G. and Ma, L.


This project examines factors affecting the uptake and internalization of E. coli O157:H7 in lettuce plants. Growth and survival of the pathogen will be evaluated according to several key variables, including pathogen strain, produce type, growth cycle phase, environmental factors, and mechanical processing. The results will improve our understanding of the factors that influence E. coli O157:H7 growth and survival in and on produce, enabling the development of enhanced risk mitigation strategies. It is anticipated that E. coli O157:H7 is internalized through the roots of seedlings or older plants when the plants are subjected to stressful conditions (such as excessive heat or restricted water/nutrients), although this route of internalization may result in the pathogens either not surviving or failing to be transported up through the plants? vascular system to their edible tissues. Internalization may occur more readily through the leaf surface, depending on the physical location of E. coli O157:H7 on the leaves, availability of nutrients, and insect-related mechanical damage to the leaf. Contaminated cutting blades used to harvest the lettuce could also serve as a tool to expose internal tissues to E. coli O157:H7, although treatment with a chlorinated water rinse soon after the contamination may reduce pathogen levels.