Purpose: The risk associated with Escherichia coli O157:H7 survival on the surface and transfer between tomatoes and common packaging house materials were the purpose of this study.
Methods: Green, unwashed tomatoes, as well as squares of materials found in the packing house environment (stainless steel, vinyl belt, and HDPE, 3 x 3 in), were spot inoculated with a five-strain cocktail of rifampin-resistant E. coli O157:H7 and dried. Survival was monitored at 15 °C (tomatoes only), 25 °C (tomatoes and squares), and temperature abuse conditions (tomatoes only) for four days. Pathogen transfer from squares to tomatoes and vice versa were evaluated in wet, 90 min dry, and 24 h dry states either immediately or 24 h later. Pathogens were recovered in buffered peptone water, and plated on tryptic soy agar with 80 ppm rifampin for enumeration and percent positive calculation.
Results: E. coli O157:H7 numbers declined 1.4 log units after 90 min drying, and continued to decline at both 15 °C, 25 °C, and during temperature ramp (from 25 °C to 15 °C over 96 h), resulting in 2.4, 1.5, and 2.6 log unit reductions by day 4, respectively. The plate counts declined from an inoculation level of 6.1 log CFU/ml to below 1.0 log CFU/ml on average after four days at 25 °C for all squares. Wet transfers (zero drying time) yielded 100% positives on day 0 and day 1. Dry transfers (90 min and 24 h drying time) from tomatoes to squares showed higher transfer rates than the converse. Interestingly, vinyl belt picked up the most pathogen cells (90 min dry), resulting in 100% positive, followed by HDPE (66.7% positive) and stainless steel (55.6% positive).
Significance: Overall, E. coli O157:H7 did not survive well on the surfaces resulting in poor dry transfers under conditions tested.