Purpose :This project seeked to understand how in vitro Salmonella biofilm production and survival on tomatoes and plastic mulch is affected by relative humidity and explained by Salmonella rdar (red, dry, and rough) morphology and quorum sensing.
Methods : Desiccators with salt slurries (lithium chloride, potassium carbonate, and potassium sulfate) were used to create controlled RH environments (~15, 50, and 100% RH). Biofilm production of six Salmonella strains were tested in microtiter plates with crystal violet. Salmonella strains were selected for survival and biofilm studies on tomatoes and plastic mulch. Salmonella samples from tomatoes at 100% RH were tested for quorum sensing.
Results : MAE110 had the most and J1890 had the least amount of biofilm production in all RH environments. MAE119 had the largest variability in biofilm production across RH. Salmonella strain MAE110 had the rdar morphotype, while other strains did not. MAE110, MAE119, and J1890 were chosen for further testing based on their varying biofilm production and rdar morphotypes. These Salmonella strains had the best survival at 100% RH at the end of 14 days on plastic mulch (4.2±0.4 to 6.0±0.7 log CFU/square) and seven days on tomatoes (5.0±0.9 to 7.1±0.2 log CFU/tomato). No biofilm production was observed on plastic mulch at 100% RH. MAE110 was the only strain to show potential biofilm production on tomatoes. Quorum sensing was not observed for any of the three Salmonella strains on tomatoes stored at 100% RH.
Significance : Better understanding of Salmonella survival on tomatoes could lead to better practices and a reduction in outbreaks. Storing tomatoes at a lower RH resulted in less Salmonella survival on tomatoes.