Efficacy of Acetic Acid or Chitosan for Reducing the Prevalence of - and O157:H7-Contaminated Leafy Green Plants in Field Systems.

Outbreaks associated with fresh-cut leafy greens continue to occur despite efforts to implement horticultural practices that minimize introduction of enteric pathogens to the crop. The experimental trials in this study were designed to examine the efficacy of an acetic acid (AA)- and chitosan-based spray treatment, applied 1 day prior to harvest, for reducing the prevalence of O157:H7 (O157) and in field-grown leafy greens contaminated at levels detectable only through enrichment culture. Responses to the treatment solution were variable and depended on the type of leafy green (leafy lettuce, spinach, or cabbage), cultivar, pathogen, and AA concentration (0.3 to 0.7%). No significant differences in O157 prevalence were found for untreated and treated cabbage heads and spinach plants ( > 0.05). In contrast, treatment significantly affected on 'Bravo F1' green cabbage and '7-Green' spinach ( < 0.05), with odds ratios of 2.2 and 3.3 for finding the pathogen on untreated versus treated greens, respectively. was also 7.1 times more likely to be found on an untreated lettuce plant than on a lettuce plant sprayed with a 0.7% AA treatment solution (95% confidence interval [CI], 4.1 to 12.2; < 0.0001). In studies addressing the efficacy of chitosan (0.1 or 0.3%), this chemical failed to reduce the prevalence of either pathogen on lettuce ( > 0.05). Similarly, spraying with 0.3% AA did not affect the prevalence of on lettuce plants ( > 0.05); however, treatment solutions with 0.4% AA reduced the likelihood of detecting in treated versus untreated plants by 6.6 times (95% CI, 2.1 to 20.9; = 0.0007). After the lettuce was harvested and hand washed, consumers failed to distinguish either visually or organoleptically between untreated lettuce and lettuce sprayed with an acetic acid solution ( > 0.05). These results indicate that acetic acid could be used to reduce the microbiological risk of preharvest leafy greens.