Diversity in biofilm formation and production of curli fimbriae and cellulose of Salmonella Typhimurium strains of different origin in high and low nutrient medium

The biofilm forming behavior of 51 Salmonella Typhimurium strains was determined in Tryptone Soya Broth (TSB) and 20 times diluted TSB (1/20TSB) at 25 degrees C and 37 degrees C. The results indicated that biofilm forming behavior is influenced by environmental conditions and associated with the origin of the strains. Clinical, outbreak-associated and retail product isolates showed dense biofilm formation in both media at 25 degrees C, and in TSB also at 37 degrees C. However, industrial isolates only showed dense biofilm formation in 1/20TSB at 25 degrees C. By enumeration of biofilm cells, LIVE/DEAD staining and SEM analysis of biofilms it was found that the ratio of cells and extracellular matrix is affected by environmental conditions. Indeed, the genes involved in curli fimbriae and cellulose production are highly induced during biofilm formation at 25 degrees C in 1/20TSB. This indicates that these are important matrix components during biofilm formation in 1/20TSB at 25 degrees C and that other factors contribute to biofilm formation of clinical, outbreak-associated and retail product isolates at 37 degrees C and/or nutrient-rich conditions.