Proliferation of Escherichia coli O157 on washed and unwashed spinach leaves

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Vegetable have recently been implicated in outbreaks of foodborne diseases. These outbreaks have led to increased scrutiny of vegetable processing and sanitation. The purpose of this study was to determine the fate of Escherichia coli O157 on washed and unwashed spinach leaves. Unwashed and washed (100 ppm sodium hypochlorite for one minute) samples were inoculated with a non-toxigenic strain of E. coli O157. The samples were dried for one hour. The total plate count (TPC) and E. coli O157 counts were taken immediately after drying and on days 3, 5, 7, 9, and 11 while stored at 4°C. The same counts were taken on days 1, 2, and 3 for samples stored at room temperature. At room temperature, differences between washed and unwashed spinach leaves were not observed. The TPC from washed and unwashed samples was similar at both temperatures. The E. coli O157 counts on both washed and unwashed leaves decreased, but there was a greater decrease on the unwashed spinach leaves (P=0.007). Although the TPC counts were similar on both washed and unwashed leaves, it is possible that the microbial communities differed on washed and unwashed leaves or the TPC did not microorganisms that would affect the survival and proliferation of E. coli O157. Enteric pathogens that contaminate vegetables after sanitation at a processing facility could negatively affect produce safety possibly due to changes in the microbial community dynamics on leaf surfaces.


This poster presentation is for the graduate student competition.


E. coli O157, food safety, vegetables, spinach, foodborne diseases