Purpose: We hypothesise that cherry tomatoes naturally produce higher levels of H2O2 in their intercellular fluid than larger tomatoes.
Methods: Around 100 cells of Salmonella were inoculated in wounds under the pericarp in both the cherry and Alicante (larger) tomatoes. Salmonella proliferation was measured after a week of incubation by plating on Xylose lysine deoxycholate agar (XLD agar). To test H2O2 levels a novel method was used. Small pieces of the pericarp (from both cultivars) totalling 2g were subjected to a pressured vacuum to infiltrate distilled water into the intercellular space. The pieces were then spun in a centrifuge to extract all fluid from the intercellular space. Samples were de-proteinised using 10kD spin columns. A fluorometric assay was then used to test the concentration of H2O2. Four biological and two technical replicas were carried out.
Results: The increase of Salmonella from one week of initial incubation was up to 104 CFU/tomato in Alicante cultivar, and 102 CFU/tomato in the cherry cultivar. The difference in Salmonella proliferation was significant (α=0.05). The cherry tomatoes showed an average of 0.76nmol/ml of H2O2 whereas the Alicante cultivar showed an average of 0.46nmol/ml. The difference in H2O2 concentration between the tomato cultivars was significant.
Significance: These findings open opportunities into genetic research of the tomato. The oOxyR gene in Salmonella activates the regulon of H2O2 inducible genes. Such pathways can be involved in Salmonella proliferation in tomatoes.