Use of a Natural Biocontrol Agent Bacillus subtilis UD1022 to Increase Crop Yield and Reduce Contamination by Listeria monocytogenes On Cantaloupes

Use of a Natural Biocontrol Agent Bacillus subtilis UD1022 to Increase Crop Yield and Reduce Contamination by Listeria monocytogenes On Cantaloupes

Summary

Cantaloupes serve as one of the major crops in the state of Delaware accounting for approximately $850,000 in estimated annual sales. However; a recent turning point for the cantaloupe industry occurred this past year when the Jensen brothers received criminal charges for growing produce that was contaminated with Listeria monocytogenes and was associated with an outbreak resulting in the deaths of 34 individuals. The purpose of this project is to evaluate the use of a plant growth promoting rhizobacteria, Bacillus subtilis UD1022, to reduce the contamination of cantaloupes by Listeria monocytogenes in the pre-harvest environment as well as in the packinghouse environment. Preliminary data has shown the ability of UD1022 to help increase crop yield through complex plant-microbe interactions that increase plant defenses toward plant pathogens. Preliminary data has also shown that UD1022 can inhibit growth of Listeria monocytogenes, in culture as well as on leaves of Romaine lettuce plants when UD1022 is inoculated onto the roots of plants. In this study pieces of cantaloupe rind were treated with UD1022 supernatant or sterile water immediately following inoculation with L. monocytogenes or after 8 h of incubation. Cantaloupe rind pieces were incubated at either 37°C, 22°C or 4°C.  In this study, we show that UD1022 supernatant has the ability to inhibit the growth of L. monocytogenes on cantaloupe rind during temperature abuse. At all temperatures L. monocytogenes growth was lowest when cantaloupe pieces were treated with UD1022 supernatant compared to controls. This inhibition was significant at room temperature (22°C) (p=0.0024). These results indicate that UD1022 may be used as a natural biocontrol agent to reduce the risk of contamination by L. monocytogenes on cantaloupe rind during times of temperature abuse in the packinghouse, during storage or transport. Studies are currently in progress to determine the ability of UD1022 to inhibit the growth of human pathogens on cantaloupe and alfalfa seeds.

Objectives/Performance Targets

The first objective, according to the original proposal, was to investigate the ability of UD1022 to prevent Listeria monocytogenes growth and biofilm formation on cantaloupe rinds at various storage temperatures such as those that occur in the packinghouse environment. This experiment has been completed and results can be found in the impacts/outcomes section. The final objective was to evaluate the effects of UD1022 treated cantaloupe seeds on seed germination and persistence of Listeria monocytogenes during plant growth in the pre-harvest environment. This experiment is currently in progress and will be completed in the next few months. In addition to investigating the use of UD1022 to inhibit the growth of L. monocytogenes on cantaloupe seeds, we are also investigating the use of UD1022 to inhibit the growth of Salmonella Agona and Escherichia coli O104:H4 on alfalfa seeds. Both isolates have been implicated in outbreaks attributed to alfalfa sprouts and we hypothesize that application of UD1022 could help reduce the risk of contamination by these pathogens and ultimately help prevent outbreaks linked to alfalfa sprouts.

Accomplishments/Milestones

The first objective of the proposal was completed in October 2014. The data for these experiments has been analyzed. Cantaloupe and alfalfa seed storage studies began in October 2014 and are still currently in progress. We have also begun experiments to determine the effects of UD1022 on germination of alfalfa seeds. In spring 2015 we will begin cantaloupe seed germination studies as well as studies monitoring the persistence of L. monocytogenes during cantaloupe growth.

Impacts and Contributions/Outcomes

The results of these experiments have demonstrated that Bacillus subtilis UD1022 has the potential to reduce the risk of contamination by L. monocytogenes on cantaloupes during temperature abuse such as that may occur in the packing house, during storage or transport. The use of UD1022 may provide a sustainable method for cantaloupe growers to protect their crops from plant pathogens as well as human pathogens in the pre-harvest environment as well as the post-harvest environment. An additional benefit to increasing the safety of cantaloupes is that UD1022 has been demonstrated to increase crop yields. This work will be presented at the Northeast Region of the American Society for Horticulture Science 2015 Annual Meeting in Newark, DE on January 6^th and 7^th. An abstract of this work will also be submitted to be presented at the International Association for Food Protection 2015 Annual Meeting in Portland, Oregon July 25^th – 28^th. We predict our future work will show that UD1022 can also be used to inhibit the growth of human pathogens on cantaloupe and alfalfa seeds.

Collaborators: