New Proprietary Post-harvest Treatment Reduces Listeria monocytogenes and Salmonella Species on Fresh Grape Tomatoes

Introduction:  Fresh produce, often consumed raw, has been repeatedly linked to foodborne illness and accounts for some of the most deadly outbreaks. Salmonella spp. (S.spp.) and Listeria monocytogenes (L.m.) are two of the most critical pathogens of concern for produce safety.

Purpose:  Ansera Analytics is developing a new proprietary post-harvest treatment for fresh produce to protect the commodity from biological hazards during distribution. The purpose of this study was to explore the treatment’s ability to reduce L.m. and S.spp. on fresh grape tomatoes.

Methods:  Fresh grape tomatoes (n = 12) were soaked in a 10⁶ CFU/ml L.m. or S.spp. solution for one minute, air-dried, and then soaked in the treatment solution for one minute. Samples were air dried to allow the material to dry. Bacterial swabs (n = 3) were collected from the tomatoes at day 0, 3, 6, and 9. All cultures were grown on nutrient agar and CFUs were enumerated at 24 h. Plates were held for 7 days.

Results:  Preliminary data suggests a clear trend towards a significant reduction in L.m. and S.spp. on treated tomatoes. Adulterated, non-treated tomatoes (control) showed confluent growth of pathogens for the majority of swabs during the 9-day sampling period, while treated tomatoes showed a 3 - 6 log CFU/ml reduction. Some swabs contained no visible colonies after 24 h but started to grow up after 2 - 4 days. This demonstrates the treatment’s inhibitory effect. Swabs from day 6 and day 9 grew less L.m. than swabs from day 3, but contained more molds.

Significance: The post-harvest treatment currently in development demonstrates the ability to reduce L.m. and S.spp. populations on the surface of fresh grape tomatoes and inhibits the pathogen’s growth for several days. The treatment has also effectively been tested on adulterated cantaloupes.