Sodium chloride maintains osmotic pressure of living cells including bacteria. Heat treatment is common for decontamination of bacteria in food. In this study, effects of NaCl on heat resistance of Salmonella Typhimurium were investigated. After cultivation in TSB containing 0.5% (TSB), 4% (4SC) and 8% (8SC) NaCl, S. Typhimurium cells were heated at 60 °C for 20 min. Total viable counts including intact cells and injured but recoverable cells determined by the plating method using TSA of S. Typhimurium cultured in 4SC and 8SC were significantly higher than those of the cells cultured in TSB. Meanwhile, changes of gene transcription were analyzed by DNA microarray. Transcription of genes involved in the colanic acid synthesis largely increased after cultivation in 4SC and 8SC. The amount of colanic acid significantly increased in the cells cultured in 4SC compared to that in M9-glucose medium. After recovery culture for 3 h, the genes involved in the phage shock response strongly up-regulated, suggesting contribution of these gene products in recovery of heat injured cells. The outcome of this study contributes to understand the mechanism of cross protection in Salmonella.
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