Role of Soil, Crop Debris, and a Plant Pathogen in Salmonella enterica Contamination of Tomato Plants

Authors: Barak Cunningham, Jeri; Liang, Anita

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/29/2008
Publication Date: 2/7/2008
Citation: Barak Cunningham, J.D., Liang, A.S. 2008. Role of Soil, Crop Debris, and a Plant Pathogen in Salmonella enterica Contamination of Tomato Plants. PLoS One. e:1657

Interpretive Summary: Background: In 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 has not been investigated. Methodology/Principal Findings: This 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 leaves or roots. The presence of X. campestris pv. vesicatoria on co-colonized tomato plants had no effect on the incidence of S. enterica tomato leaf contamination. However, growth of S. enterica in the tomato leaves occurred on co-colonized plants in the absence of plant disease. Conclusions/Significance: S. enterica populations decline in fallow soil and the tomato roots, although sowing seed in contaminated soil can lead to contamination of the tomato leaves. S. enterica leaf populations declined more slowly than those in fallow soil or the tomato roots. In the absence of plant disease, presence of the 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.

Technical Abstract: Background: In 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 has not been investigated. Methodology/Principal Findings: This 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 populations decline in fallow soil and the tomato rhizoplane, although sowing seed in contaminated soil can lead to contamination of the tomato phyllosphere. S. enterica phyllosphere populations declined more slowly than those in fallow soil or the tomato rhizoplane. 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.