Quantifying Transfer Rates of Salmonella and Escherichia coll O157:H7 between Fresh-Cut Produce and Common Kitchen Surfaces

Cross-contamination between foods and surfaces in food processing environments and home kitchens may play a significant role in foodborne disease transmission. This study quantifies the cross-contamination rates between a variety of fresh-cut produce and common kitchen surfaces (ceramic, stainless steel, glass, and plastic) using scenarios that differ by cross-contamination direction, surface type, produce type, and drying time/moisture level. A five-strain cocktail of rifampin-resistant Salmonella was used in transfer scenarios involving celery, carrot, and watermelon, and a five-strain cocktail of rifampin-resistant Escherichia coli 0157:H7 was used in transfer scenarios involving lettuce. Produce or surface coupons were placed in buffer-filled filter bags and homogenized or massaged, respectively, to recover cells. The resulting solutions were serially diluted in 0.1% peptone and surface plated onto tryptic soy agar with 80 ng/ml rifampin and bismuth sulfite agar with 80 ng/ml rifampin for Salmonella or sorbitol MacConkey agar with 80 ng/ml rifampin for E. coli 0157:H7. When the food contact surface was freshly inoculated, a high amount (>90%) of the inoculum was almost always transferred to the cut produce item. If the inoculated food contact surfaces were allowed to dry for 1 h, median transfer was generally >90% for carrots and watermelon but ranged from < 1 to ~70% for celery and lettuce. Freshly inoculated celery or lettuce transferred more bacteria (~2 to -25% of the inoculum) compared with freshly inoculated carrots or watermelon (approximately