Survival of Tomato Outbreak Associated Salmonella Serotypes in Soil and Water and the Role of Biofilms in Abiotic Surface Attachment.

Salmonella serotypes linked to tomato-associated outbreaks were evaluated for survival in soil and water over a 40-day period. Salmonella enterica serotypes Anatum, Baildon, Braenderup, Montevideo, Newport, and Javiana were inoculated separately into sterile soil and water, followed by plating onto TSAYE and XLT4 at 10-day intervals. Biofilm production by Salmonella serotypes was measured on both quartz particles (soil surrogate) and glass coverslips, and was evaluated using a crystal violet dye assay. Salmonella populations in soil and water over 40 days indicated no significant differences between Salmonella serotypes tested (p > 0.05). Over a 40-day period, there was a 1.84 ± 0.22 log CFU/g and 1.56 ± 0.54 CFU/mL decrease in populations of Salmonella in soil and water, respectively. Enumeration indicated that Salmonella population fluctuated in water but decreased linearly in soil. All serotypes tested produced the "red dry and rough" morphotype on Congo Red agar. Biofilm produced by all the Salmonella serotypes tested was significantly different on quartz particles than on glass coverslips (p < 0.0001), indicating that material and surface characteristics could affect biofilm development. The ability of Salmonella serotypes to persist in soil or water and attach to abiotic surfaces through biofilm formation affirms that contact surfaces, soil, water, and sediment should be considered as possible sources of cross-contamination in the farm environment.