Survival of Virulent and Mutated Salmonella enterica Newport and Typhimurium Strains on Tomato Plants and in Soils

Introduction: Outbreaks of foodborne diseases caused by enteric pathogens have increasingly been associated with fresh produce, like tomatoes. Salmonella enterica has been reported to be the leading cause of these outbreaks in the United States. However, the survival mechanism of Salmonella on/in tomato plants as well as in agricultural soils is still obscure.

Purpose: To compare the survivals of different attenuated/mutated S. Newport (SeN) and S. Typhimurium (SeT) strains with their virulent wild type strains on/in tomato plants and in soils.

Methods: In this study, survival of nine Salmonella strains in soils (Exp. 1), and on/in tomato leaves (Exp. 2) were investigated, which include virulent strains SeN J1892 and SeT ATCC14028 and their corresponding attenuated/mutated strains N17 (SeN, ΔtolC::kan), T770 (SeT, pSLT-), TJSG (SeT, Δbcs::kan), T0 (SeT, ΔagfB::kan), T1 (SeT, ΔagfC::kan), T2 (SeT, ΔompL::kan), and T3 (SeT, ΔyihT::kan). In Exp. 1, Salmonella solution of each strain was mixed into soils collected from tomato fields to reach initial bacterial concentration of about 10⁶ CFU/g. The bacterial population was tested 1, 4, 8, 15, 22, and 28 days after inoculation. In Exp. 2, inoculation was performed by dipping tomato leaves in 10⁸ CFU/ml Salmonella solution of each strain for 10s. The bacterial population on/in leaf samples was tested 1, 7 and 14 days after inoculation.

Results: There was no significant difference among the tested Salmonella strains for bacterial survival in soils. The population decline rates of strains N17, T770, T2 and T3 on leaf surface were significantly higher than that of their wild type strains. Similarly, the populations of strains N17, T1, T2 and T3 in inoculated tomato leaves decreased more quickly than that of the wild type strains.

Significance: These results would benefit studies about Salmonella and tomato interaction, and bring clues to reduce Salmonella contamination on tomatoes.