Abstract
BackgroundIn the U.S., tomatoes have become the most implicated vehicle for produce-associated Salmonellosis with 12 outbreaks since 1998. Although unconfirmed, trace backs suggest pre-harvest contamination with Salmonella enterica. Routes of tomato crop contamination by S. enterica in the absence of direct artificial inoculation have not been investigated.Methodology/Principal FindingsThis work examined the role of contaminated soil, the potential for crop debris to act as inoculum from one crop to the next, and any interaction between the seedbourne plant pathogen Xanthomonas campestris pv. vesicatoria and S. enterica on tomato plants. Our results show S. enterica can survive for up to six weeks in fallow soil with the ability to contaminate tomato plants. We found S. enterica can contaminate a subsequent crop via crop debris; however a fallow period between crop incorporation and subsequent seeding can affect contamination patterns. Throughout these studies, populations of S. enterica declined over time and there was no bacterial growth in either the phyllosphere or rhizoplane. The presence of X. campestris pv. vesicatoria on co-colonized tomato plants had no effect on the incidence of S. enterica tomato phyllosphere contamination. However, growth of S. enterica in the tomato phyllosphere occurred on co-colonized plants in the absence of plant disease.Conclusions/Significance S. enterica contaminated soil can lead to contamination of the tomato phyllosphere. A six week lag period between soil contamination and tomato seeding did not deter subsequent crop contamination. In the absence of plant disease, presence of the bacterial plant pathogen, X. campestris pv. vesicatoria was beneficial to S. enterica allowing multiplication of the human pathogen population. Any event leading to soil contamination with S. enterica could pose a public health risk with subsequent tomato production, especially in areas prone to bacterial spot disease.
Highlights
In recent years, tomatoes have been one of the most common vehicles of produce-associated Salmonellosis
To test the longevity of the S. enterica population in soil and whether these cells could contaminate plants, soil was irrigated with S. enterica contaminated water, seeds were sown at weekly intervals, and plants were examined for S. enterica
S. enterica was not recovered from control plants
Summary
Tomatoes have been one of the most common vehicles of produce-associated Salmonellosis. The route of contamination remains indefinable, probable suspects exist: water, soil, animal waste, and insects [4]. It has been shown in a hydroponic system that S. enterica can contaminate entire tomato plants following direct root inoculations [5]. Tomato fruits can be contaminated with S. enterica following direct flower inoculations [6]. These routes of inoculation probably do not reflect the natural contamination route of field grown tomatoes. The colonization or contamination of tomato plants in the absence of direct artificial inoculation has not been investigated thoroughly. Routes of tomato crop contamination by S. enterica in the absence of direct artificial inoculation have not been investigated
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