Curli production influences cross-contamination by Escherichia coli O157:H7 when washing fresh-cut Romaine lettuce.

Escherichia coli O157:H7 expresses extracellular proteins called curli that are essential for surface colonization. Transfer rates of E. coli O157:H7 0018 + (curli + ), and 0018-(curli-) from inoculated to noninoculated lettuce pieces during washing were quantified in this study. Romaine lettuce pieces were inoculated with ~6 log CFU on just the surface, just the cut edges, or both surface and cut edges. Samples were dried for 2 h in a biosafety cabinet and then washed with ten (10) noninoculated lettuce pieces in 500 mL of water for 30 s. The curli-strain was more readily removed (3 log reduction) compared to the curli + (1 log reduction) when only the lettuce surface was inoculated (p > 0.05). The same was true when only the lettuce piece edge was inoculated (p > 0.05), although the magnitude of the reduction was less. There was no significant difference in reduction of...