Irrigation regime, fruit water congestion and produce safety: parameter optimization to reduce susceptibility of tomatoes and peppers to post-harvest contamination, pathogen transfer and proliferation of Salmonella.

Irrigation regime, fruit water congestion and produce safety: parameter optimization to reduce susceptibility of tomatoes and peppers to post-harvest contamination, pathogen transfer and proliferation of Salmonella.

Jan. 1, 2011 - Dec. 31, 2012

2011-128

$188,271.00

Max Teplitski, Ph.D.
University of Florida

Jerry Bartz, Ph.D., George Hochmuth, Ph.D.

Final Report

Recent multi-state outbreaks of vegetable-borne gastrointestinal illnesses demonstrate that human pathogens can contaminate produce at any stage of production. The fact that the outbreaks have been sporadic and the uncertainty regarding sources and routes of contamination argue for the possibility that some event(s) during the production cycle make vegetables more susceptible to contamination from environmental sources of pathogens. We
hypothesize that irrigation-determined physical properties of tomatoes and peppers (fruit wetness, fruit water congestion, etc) may make them more vulnerable to contamination from various environmental sources, including transfer from rubber gloves or wiping cloths. Fruit wetness and fruit water congestion also increase susceptibility of vegetables to plant pathogens, and the association with plant pathogens has been well-documented to promote
growth of Salmonella in vegetables. The overall goal of this project is to test how irrigation determined physical properties of tomatoes and peppers affect vulnerability of produce to infections by Salmonella. Upon completion of this project, we expect to have defined an optimal irrigation regime under which yields are maintained, yet the vulnerability of produce to contamination and proliferation of Salmonella are reduced. Following a successful completion of the first two production seasons, a full scale on-farm demonstration will be carried out.

Technical Abstract

As the number and severity of produce‐borne gastroenteritis outbreaks increase, we are coming to recognize that enteric pathogens can escape surface sanitation leading to contaminated fruits, vegetables and sprouts in the marketplace. The outbreaks associated with produce appear to be sporadic and do not generally result from an oversight by a producer or handler. We hypothesize that physical properties of produce, which are determined by the irrigation regime pre‐harvest, affect susceptibility of tomatoes and peppers to environmental sources of pathogens. We propose that by augmenting growing practices, safety of produce can be improved through the reduction in susceptibility of fruits to accidental sources of enteric pathogens. The overall goal of this proposal is to increase safety of vegetable produce by testing how irrigation regime pre‐harvest, fruit wetness and water congestion at harvest affect susceptibility of produce to post‐harvest contamination with Salmonella. The optimization of these parameters will promote produce safety either directly (by providing a less hospitable environment for Salmonella or by reducing transfer of pathogens from rubber gloves or wiping cloths onto fruits) or indirectly (by reducing injury from soft‐rot bacteria or sour rot pathogens, which increase growth of human pathogens on produce). The following specific objectives will help us reach this goal: Objective 1. To reduce post‐harvest susceptibility of tomatoes and peppers to Salmonella through the optimization of irrigation regime and fruit wetness at harvest With this objective, we will test how differences in physical properties of the fruit resulting from different irrigation regimes pre‐harvest and fruit wetness at harvest will affect susceptibility of fruit to contamination with Salmonella from rubber gloves and/or wiping cloths. Objective 2. To determine whether water congestion (with or without post‐harvest soft rot or sour rot decay) is a risk factor for Salmonella colonization or internalization. In the field, congestive water in fruits may result from root uptake, rainfall, saturated atmospheres or harvest‐related injuries. Experiments proposed here will determine whether fruit water congestion with or without postharvest decay is a risk factor for Salmonella
contamination and/or internalization in tomato and pepper tissues under the simulated production line conditions. We will compare survival of Salmonella in water‐congested fruit at three stages of ripeness (green commercial harvest, breaker/pink (commercial vine‐ripe) or fully red). Because water congestion is known to predispose produce to infections with plant pathogens, and because soft‐rot pectobacteria and sour rot yeasts are known to promote
growth of Salmonella in fruit tissues under laboratory conditions, we will test how these two factors affect proliferation of Salmonella in tomatoes and peppers post‐harvest. Objective 3. To define the role for spoilage bacteria in contamination of fruit with Salmonella. In soft rots caused by Pectobacteria, Salmonella grows to final populations that are 10‐100x higher than in mechanically damaged fruit. It is not yet known whether plant pathogens, when
present at low numbers, will also promote contamination of produce with Salmonella. We will determine the mechanisms by which two common plant pathogens of tomato and pepper promote susceptibility of fruit to contamination and internalization of Salmonella.