Purpose: Quantify the transfer of Salmonella from inoculated unwashed green tomatoes to clean, dirty (wet or dry) cloth, and vice versa.
Methods: Green tomatoes were spot inoculated with a rifampicin resistant cocktail of Salmonella spp. (107 CFU/ml). Inoculated tomatoes were touched with 8 x 8 cm cotton cloth (clean, dirty dry, dirty wet) 0, 1, or 24 h post-inoculation. Three contact times (5, 10, 20 s), and three degrees of rubbing (none, mild, vigorous) were evaluated. The cloths were dirtied by rubbing with a tomato leaf for 20 s (wet) and dried for 1 h (dry). Salmonella was enumerated on tryptic soy agar containing rifampicin, followed by enrichments when necessary. Transfer coefficients (TCs) were calculated by dividing Salmonella CFU on the touched surface by that on the inoculated surface. The transfer direction was then reversed by touching uninoculated tomatoes with an inoculated cloth. Ten replicates were used for sampling.
Results: The highest transfer rates from inoculated tomato to cloth occurred when the inoculum was wet, regardless of cloth condition. Contact time and degree of rubbing did not significantly affect the TCs. TCs from inoculated cloth to tomato was highest when the tomato was touched on inoculated clean cloth, without rubbing, TCs = 0.48±0.1. The TCs were greatly reduced when tomatoes were contacted on inoculated dirty dry (TCs = 0.002) or wet (TCs = 0.007) cloths. Detectable levels of Salmonella were not transferred from inoculated cloths to tomatoes 1 or 24 h post-inoculation.
Significance: Salmonella transfer can occur between tomatoes and cloth especially when the inoculum is wet; there exists a potential for cross contamination when using cotton cloth to remove dirt and debris from the field.