The Role of Aggregative Fimbriae and Cellulose in the Persistence of Salmonella Typhimurium on Tomatoes

Introduction:  The rise of produce-linked salmonellosis outbreaks has directed attention towards the persistence of Salmonella spp.  A complex phenotype of Salmonella spp., known as rdar (red dry and rough), has been linked to increased resistance to desiccation and environmental stress.  Thin aggregative fimbriae, cellulose, and production of other extracellular polysaccharides mediate the rdar phenotype, as well as attachment and biofilm formation.  The deletion of the aggregative fimbriae and cellulose biosynthesis genes results in a loss of the rdar phenotype.  The comprehension of how aggregative fimbriae and cellulose alter the biofilm formation and persistence of Salmonella spp. on the tomato surface will indicate their role in their environmental fitness.

Purpose:  The aim was to study the role of aggregative fimbriae and cellulose of S. Typhimurium on the tomato surface to further characterize the genetic basis of the surface interactions between Salmonella spp. and produce.  

Methods:  Analysis of the biofilm formation of S. Typhimurium (ATCC 14028) and S. Typhimurium mutants deficient in thin aggregative fimbriae and/or cellulose production were completed in both polystyrene and plant surface environments.  Diluted solutions of the Salmonella strains in colonization factor antigen (CFA) media were incubated in 96-well polystyrene plates at 30°C for 24 hours.  The plant surface assays involved soaking the plant segments in the inoculated CFA media for 24 hours at 30°C.  After the 24 hours, the 96-well plates or the produce segments were stained with crystal violet.  The biofilms were then solubilized with acetic acid and absorbance at 595 nm was recorded. 

Results:  The deletion of aggregative fimbriae and cellulose biosynthesis genes does significantly reduce the biofilm formation of S. Typhimurium on polystyrene and plant surfaces, indicating that both components play a role in environmental persistence. 

Significance:  The results support the importance of aggregative fimbriae and cellulose in the environmental fitness S. Typhimurium to the surface of tomatoes.