Survival of Attenuated Escherichia Coli O157:H7 ATCC 700728 in Field Inoculated Lettuce

From 1995 through 2006, 22 outbreaks of Escherichia coli O157:H7 were associated with consumption of leafy green vegetables. For reasons unknown, most of the outbreaks have been associated with lettuce that was harvested in late summer or early fall. <P>To reduce the potential for further outbreaks we need to have a better understanding of how E. coli O157:H7 survives in fields of growing lettuce. To accomplish this we have used a non-pathogenic strain of E. coli characteristics that are similar to the pathogen to inoculate growing lettuce plants in the field. Lettuce plants were inoculated (mock contamination event) a single time 4 weeks after planting. <P>
Our preliminary data suggest that after a contamination event E. coli does not survive very well. Large, rapid decreases in numbers of the organism are observed on each lettuce plant. However, small number of E. coli do survive on the lettuce plants for much longer periods and in two trials up to and including the time of harvest (about 7 to 9 weeks after planting and 3 to 4 weeks after introduction of E. coli). <P>
The proposed research will build on these preliminary data with two field trials in 2009 that will compare both drip and sprinkler irrigation and spring (mid-May) and late summer (mid-July) plantings.<P>
Our long-term goal is to generate data that will help inform growers of strategies that could mitigate the risk of the organism surviving on lettuce after a contamination event.