Airborne Soil Particulates as Vehicles for Salmonella Contamination in Tomatoes

Introduction: Several outbreaks of salmonellosis have been associated with the consumption of fresh tomatoes.  Salmonella serotypes have been shown to survive in soil and may persist in the farm environment.  However, tomato contamination routes in the field environment remain unclear.

Purpose: The potential of soil particulates as vehicles of contamination of tomato blossoms and fruits was examined.

Methods:   Salmonella Newport (containing the pNSTrc-lux plasmid) was grown in TSB (24 h; 37°C) and centrifuged.  The cell pellet was mixed with soil and dried (9 CFU/g of soil).  Using compressed air, the Salmonella/soil mixture was delivered to tomato blossoms.  One week after treatment, the blossoms were removed from the plant, pummeled in peptone water, and plated onto XLT4 Agar.  Additionally, treated blossoms were imaged with a high sensitivity CCD camera to determine the location of bioluminescent Salmonella.

Results: When the S. Newport/soil mixture was applied using compressed air, 29% of blossoms were positive for pathogen presence. More than half of the positive blossoms (51%) developed into fruit that were also positive for the presence of S. Newport. Fruit and calyx tissue were positive for S. Newport presence even after surface sterilization. Biophotonic imaging revealed that Salmonellacells were transferred to the petals, stamen and pedicel of the blossom.

Significance: Highly contaminated airborne soil particles may be capable of transferring Salmonella to tomato blossoms. Salmonella presence in  blossoms may result in contaminated tomato fruits.