Non-thermal methods to disinfect enterohemorhagic Escherichia coli contamination in salad vegetables

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A strain of enterohemorrhagic Escherichia coil O157 was transformed by the plasmid which contained the green fluorescence protein gene. Artificially contaminated lettuce was produced by soaking the leaves in the suspension of the bacterium. Neglecting preexisting bacterial flora the number of O157 were accurately counted for their fluorescence under irradiation of UV. Throughout this research various kinds of chemical reagents and treatment-conditions were examined for disinfecting effects. Heated shell-powder solution showed strong bactericidal activity on lettuce rather than hypochlorite. A part of the inoculum seemed to have invaded to lettuce organization inside where the drug is difficult to reach and perfectly kills it. The O157 organisms were killed in 8-24 hour, when the lettuce was preserved at the low temperature after soaking in the shell-powder solution. Biopreservation is becoming attractive method for food safety. Although bacteria showing inhibitory effects against O157 were isolated from the human fecal specimens, it was not found among normal bacterial flora of foods throughout the experiments. It was suggested through some preliminary experiments that pulsed power electric discharge could possibly reduce the level of O157 contamination on lettuce.