Influence of Microbial and Host Cell Sublethal Heat Stress on S. Typhimurium Gene Expression

Environmental stress contributes to the outcome of infection by impacting both microbial virulence and host susceptibility to infection. Thermal processing, commonly used for decontamination of poultry in the food industry, may elicit sublethal stress on resistant serovars of Salmonella. We employed traditional heat shock temperatures (42 and 48ºC), similar to avian body temperature and poultry processing conditions, to study gene expression of Salmonella enterica serovar Typhimurium. Microarray analysis indicated that thermal shock at 42°C and 48°C induced expression of SPI-2 and SPI-5 genes, whose products are required for adhesion and survival. However, SPI-1 genes, responsible for invasion of Salmonella into host cells, were down-regulated following exposure to 42°C and 48°C. Bacterial adhesion assays showed greater adhesion of heat-stressed S. Typhimurium to Caco-2 cells compared to non-stressed bacteria. In addition, subjecting Caco-2 cells to mild heat shock (39°C), which is similar to human fever, enhanced host cell susceptibility to bacterial adhesion. Data indicate that thermal stress enhances bacterial colonization and host cell susceptibility to adhesion during S. Typhimurium infection. Several different hurdles methods are used in the food industry to combat foodborne pathogens on meat surfaces. One of these methods is thermal treatment. The objective of our study was to test the effect of heat stress on the gene expression of Salmonella. We tested traditional heat shock temperatures (42 and 48ºC), similar to avian body temperature and poultry processing conditions for this study. We grew the Salmonella at 30 ºC overnight. After this, we transferred to fresh media and grew the cells to mid-log phase. The cells were then subjected to heat shock and gene expression analysis using microarrays was carried out. We found an induced gene expression profile of genes involved in adhesion and repression in genes involved in invasion. We followed up this study by tissue culture analysis to test if heat stressed Salmonella adhere better to intestinal Caco-2 cells and found that there was increased adhesion but decreased invasion.