Purpose: Comprehension of environmental factors controlling the interaction between tomato plants and Salmonella Typhimurium, and identification of effective control methods are a priority for preventing new epidemics.
Methods: Three-week-old tomato plants were sprayed with a suspension of ST, or cotyledons were clipped with scissors contaminated with the pathogen. Grown at high relative humidity (80%) and low temperature settings (20°C/15°C), survival in planta of ST populations was studied weekly until the ripening stage through bacterial quantification in plant tissues.
Results: The first week following spray inoculation, ST survived in the phyllosphere of all inoculated tissues; however, the pathogen was detected internally only in foliar tissues. Fourteen days post-inoculation, ST was detected on the surface and inside inoculated leaves, and its population stabilized at a density of 106 CFU per plant, without migration of the bacteria into the stem. Fourteen days after cotyledon inoculation by clipping, the bacterial population stabilized at a density of 105 CFU per plant. ST was still restricted to the inoculation point despite a significant increase of the internal population 21 days after the introduction of the pathogen (P < 0.01). A library of 4,182 small molecules was screened against ST. Eleven compounds killed ST with a minimal inhibitory concentration between 5 μM and 400 μM, and seven of these were bactericidal against multiple Salmonella serotypes.
Significance: This is the first investigation to demonstrate the inability of ST to colonize tomato at high relative humidity and low temperature. Further, despite the broad range of resistance of ST to antimicrobials, promising anti-ST candidates were found.