Transfer of Escherichia coli O157:H7 to Iceberg Lettuce via Simulated Field Coring
2009
The field-core (cut and core) harvesting technique used for iceberg lettuce was evaluated as a potential means of cross-contamination with Escherichia coli O157:H7. Chlorinated water treatment was evaluated for its efficacy in removing or inactivating the pathogen on the blade portion of the field coring device and on cored lettuce. Field coring devices inoculated by immersing blades in soil containing E. coli O157:H7 at 3.74 or 6.57 log CFU/g contained 3.13 and 4.97 log CFU per blade, respectively. Treatment of inoculated field coring device blades by immersing in chlorinated water (200 μg/ml total chlorine) for 10 s resulted in a reduction of 1.56 log CFU per blade, which was 1.42 log CFU per blade greater than that achieved using water, but insufficient to eliminate the pathogen on blades. Field coring devices inoculated by contacting soil containing E. coli O157:H7 at 2.72 and 1.67 log CFU/g, then repeatedly used to cut and core 10 lettuce heads, transferred the pathogen to 10 and 5 consecutively processed heads, respectively. Lettuce cores remained positive for the pathogen after spraying with 100 μg/ml free chlorine for 120 s at 2.81 kg/cm2 (40 lb/in2), regardless of the inoculum level. The number of E. coli O157:H7 recovered from inoculated lettuce cores treated for 10 s with chlorine was significantly (P <or= 0.05) different from the number recovered from tissues treated with water. Dipping contaminated field coring devices in chlorinated water may not be effective in killing the pathogen and controlling cross-contamination from head to head. Spraying contaminated lettuce with chlorinated or untreated water reduces but does not eliminate E. coli O157:H7.
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