Survival of Salmonella enterica Newport in Ralstonia solanacearum - Infected Tomato

Introduction: The Eastern Shore of Virginia (ESVA) is responsible for 80% of Virginia’s tomato production.  Over the past decade, the ESVA has been implicated in at least four outbreaks of Salmonellosis associated with tomato, all originating from the same strain, Salmonella enterica serovar Newport.  In addition to S. Newport contamination, the devastating plant disease, bacterial wilt, caused by the phytopathogen, Ralstonia solanacearum, is the most severe market disease of tomato on the ESVA and threatens the sustainability of ESVA tomato industry.  

Purpose: Due to the ESVA’s endemic population of R. solanacearum and S. Newport, the purpose of this study was to investigate the association between these two pathogens. The survival of S. Newport within tomatoes, symptomatic and asymptomatic for bacterial wilt, was examined. 

Methods: Tomato fruit were collected from plants expressing symptoms of bacterial wilt (symptomatic) and plants not expressing bacterial wilt symptoms (asymptomatic) on the ESVA during the 2011 and 2012 summer growing season.  Following collection, fruit were inoculated with 8 log CFU/ml S. Newport via vacuum infiltration and incubated for 48 hours at 13°C.  S. enterica within the internal fruit tissues was then quantified by surface sterilizing and homogenizing the fruit, and plating the homogenate onto XLT-4.  ANOVA was used to analyze results and means were separated using Tukey’s HSD at α = 0.05. 

Results: S. enterica recovery was significantly greater in fruit originating from asymptomatic (5.15 log CFU/g) versus symptomatic (4.91 log CFU/g) plants (n = 50; P = 0.0127). Fruit collected from asymptomatic plants also had a significantly higher internal pH (4.60) than fruit collected from symptomatic plants (4.37; P < 0.0001). 

Significance: These results suggest that R. solanacearum affects internal tomato fruit pH, which may reduce S. Newport survival in the fruit.  This study supports previous research findings reporting phytopathogen influence on human pathogen survival in fruits and vegetables.