Purpose: A series of Salmonella enterica genes were investigated in S. Newport associated with tomato seedling leaves.
Methods: To evaluate the Salmonella response in the tomato phyllosphere, sterile three leaved-seedlings of tomato cv. Heinz were challenged with five log CFU S. Newport/mL, delivered as 10×1 µL spots on leaf surfaces. Samples were collected six hours post-inoculation and cells immediately fixed in RNAProtect Bacteria. Total RNA was extracted and cDNA synthesized for amplification with primers targeting 14 genes needed for ROS mitigation (soxR, marA), nitric oxide detoxification (yeaR, ygbA, yoaG, yjbE), antimicrobial stress tolerance (marA, wza), tryptophan metabolism (trpD, trpE), carbon metabolism (nmpC, lamB), anaerobic conditions (ttrA, hcp) and STM1808, on an ABI Step-One Plus using SYBR as a reporter. Relative expression was compared to cells grown on Tryptic Soy Agar. Data was analyzed using the ddCt method with rpoD as an endogenous control.
Results: Salmonella Newport, epiphytic on tomato leaves, presented a significantly different gene expression profile than S. Newport on nutrient agar. A priori comparisons report genes that are important for antibiotic resistance, biofilm formation, and NO stress. The genes marA, trpD, trpE, wza, yeaR, ygbA, hcp and yjbE were expressed at significantly higher levels on tomato compared to nutrient agar, with a greater than eight-fold increase (p<0.05). Significant down-regulation of genes associated with carbon metabolism nmpC and lamB was also observed with a greater than or equal to two-fold reduction (p<0.05).
Significance: Understanding how enteric pathogens and plants mutually respond is crucial to fully describing these interactions; the knowledge of which can aid in augmenting pre-harvest risk analysis models and Good Agricultural Practices.