Journal of Agriculture & Life Sciences

Survival of Escherichia coli O157:H7 on Lettuce Harvested from Fields Irrigated by Different Irrigation Systems and Stored under Different Conditions
Libin Zhu, Vijay K. Juneja, Jorge M. Fonseca, Sadhana Ravishankar

Abstract
The objective of this study was to investigate the survival of Escherichia coli O157:H7 on iceberg and romaine lettuces harvested from fields irrigated using drip, furrow and sprinkler irrigation systems and stored under environmental conditions simulating the growing regions. Lettuce samples were inoculated with E. coli O157:H7 and stored under 3 different conditions of temperature and relative humidity (RH) combinations for 10 days. Samples were taken at 6 time points during storage to enumerate the surviving E. coli O157:H7. Neither lettuce types nor irrigation systems had a significant effect on E. coli survival. The population increased 2-3 logs and 1-2 logs when samples were stored at 26C, 40% RH and 10C, 60% RH, respectively. There was no change in E. coli O157:H7 population when stored at 4C, 60% RH. The population on mature lettuce was 0.5 log higher than that on baby lettuce after 5-day storage at 26C, 40% RH.

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