In response to continued foodborne outbreaks and recalls, two separate studies were conducted to assess the importance of various unit operations in spreading E. coli O157:H7 during production of fresh-cut leafy greens. Initially, E. coli O157:H7 transfer from a contaminated shredder and conveyor belt to previously uncontaminated iceberg lettuce, wash water, and the equipment was quantified during pilot-plant production of fresh-cut lettuce using 9.1 kg of dip-inoculated radicchio (106 CFU/g, colored surrogate for iceberg lettuce) to contaminate a pilot-plant-scale shredder or conveyor. After processing 90.7 kg of previously uncontaminated lettuce, average E. coli O157:H7 populations on the shredder and conveyor belt decreased from 3.7 to 0.9 and from 4.1 to 2.5 log CFU/100 cm2, respectively. E. coli O157:H7 levels in twenty 4.5 kg batches of lettuce collected after exiting the contaminated shredder and conveyor also decreased significantly (P < 0.05) from 2.7 to 0.9 and from 1.8 to 0.9 log CFU/g during processing. Thereafter, E. coli O157:H7 transfer from a single inoculated lettuce leaf (6.9 log CFU/g) to wash water was assessed at different water velocities in a custom-made pipe system. Shedding of E. coli O157:H7 from lettuce was significantly greater at a laminar flow rate of 0.01 m/s (5.1 log CFU) (P < 0.05) compared to turbulent flow at 0.07 m/s (3.8 log CFU) and lower laminar flow at 0.005 m/s (3.2 log CFU) with numbers of E. coli O157:H7 peaking in the water after 10, 4, 4, and 3 s at flow rates of 0.005, 0.01, 0.04, and 0.540 m/s, respectively. All of these findings will be useful in the development of bacterial transfer models for current and future risk assessments.
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