Salmonella biofilms

Biofilm formation by Salmonellaspp. is a problem in the food industry, since biofilms may act as a persistent source of product contamination. Therefore the aim of this study was to obtain more insight in the processes involved and the factors contributing to Salmonellabiofilm formation. A collection of SalmonellaTyphimurium clinical, outbreak-related and retail product isolates, was used to determine biofilm formation capacity and to identify cellular parameters contributing to surface colonisation. The results revealed dense biofilm formation by these isolates at 25 °C and 37 °C in nutrient-rich media. However, in nutrient-low media dense biofilm formation was only observed at 25 °C with industrial isolates. In addition, temperature and medium composition were also found to influence biofilm morphology and composition. At nutrient-low conditions at 25 °C the biofilm consisted of cell clusters encapsulated by an extracellular matrix composed of curli fimbriae and cellulose. In nutrient-rich conditions a monolayer of cells with little to no extracellular matrix were observed, with a prominent role for type 1 fimbriae. This type of fimbriae was only expressed in a subset of strains and appeared to contribute to initial attachment of Salmonellacells ultimately leading to dense biofilm formation. This study also indicated that biofilm formation differs between and within the Salmonellaserovars Typhimurium, Derby, Brandenburg and Infantis, isolated from meat processing environments. And, for all serovars biofim formation contributed to the survival on stainless steel surfaces and biofilm cells were less susceptible to peracetic acid disinfection treatments. This latter effect was specifically observed in the presence of organic matter, which drastically decreased the activity of peracetic acid conceivably resulting in low level exposure of the bacterial flora facilitating survival. Furthermore, single and repeated exposure to sub-lethal concentrations of the disinfectant benzalkonium chloride rapidly selected for resistant variants. In conclusion, the results obtained in this study may contribute to the development of better strategies for Salmonella control in food processing environments.