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Abstract
Escherichia coli O157:H7 is a major foodborne pathogen often linked to fresh produce, especially romaine lettuce. This study examined the efficacy of ascaroside #18 (ascr#18) as a pre-harvest treatment to reduce E. coli O157:H7 contamination on romaine lettuce. Plants were treated with ascr#18 via foliar spray or soil drench at three concentrations (0.01 µM, 0.1 µM, and 1 µM) before inoculation with E. coli O157:H7. Pathogen populations were enumerated on Days 0, 3, and 7. Foliar spray treatments achieved greater reductions than soil drench application, with the highest reduction (2.21 log MPN/head) at 0.1 µM on Day 0 (8-10 days after initial ascr#18 treatment). Although ascr#18 demonstrated significant potential in reducing E. coli O157:H7 contamination when compared to the control, differences among concentrations were not significant (p > 0.05). Future studies should explore a broader concentration range to optimize its use in commercial leafy green production. INDEX WORDS: Romaine lettuce, ascr#18, E. coli O157:H7, Preharvest treatment, Food safety