Intercellular production of Hydrogen peroxide in Solanum lycopersicum: an immune response to Salmonella infection

Produce associated gastroenteritis in recent years has become more associated with fruits and vegetables rather than raw meat and dairy, with thousands of deaths per year recorded. Outbreaks of Salmonella have been reported from a multitude of vegetables such as lettuce, spinach and tomatoes. Many of these outbreaks are the result of infection via non-typhoid Salmonella species such as Salmonella enterica sv. Typhimurium. The ecology of Salmonella as a human pathogen via vegetable hosts is increasingly being studied, however much is still unknown. Studies have shown that Salmonella may proliferate in both the rhizosphere and phyllosphere of the tomato plant Solanum lycopersiscum. In tomatoes, Salmonella has varying levels of proliferation success depending on the variety of tomato in question. Previous studies had shown that tomatoes of the cherry variety were significantly more resistant to Salmonella proliferation than larger varieties. S. lycopersicum var. cerasiforme and var. alicante were inoculated with Salmonella enterica (LT2) sv. Typhimurium and allowed to incubate for 72 hours. Following this, tomatoes were homogenised and samples plated on XLD. This study found that Salmonella ability to proliferate in var. cerasiforme was significantly different (α=0.05) when compared to var. alicante. With Salmonella proliferating up to a 1 log more in var. alicante than in var. cerasiforme. This study suggested that this difference was due to an innate difference in immune response efficacy between var. cerasiforme and var. alicante. Studies regarding plant immune responses have shown that production of hydrogen peroxide is a common response to microbial attack. Using a novel methodology, this study extracted the intercellular fluid from the tomato fruit in both var. alicante and var. cerasiforme. Analysis via fluorometric quantification found that var. cerasiforme contained significantly higher amounts of hydrogen peroxide in its intercellular fluid than var. alicante. These data suggest that the inherent and increased resistance to Salmonella proliferation in var. cerasiforme compared to var. alicante is at least in part due to its increased levels of hydrogen peroxide in its intercellular fluid.