Heat injury and recovery in Salmonella

Heat treatment is commonly used for sterilizing food. The higher the treatment temperature, the greater the sterilization efficiency; however, protein denaturation of food can result. Mild heat treatment may only sublethally injure bacterial cells. Moreover, sublethally heat-injured Salmonella in food can recover under favorable conditions, leading to foodborne illness. To elucidate the molecular mechanism of recovery from heat injury, global changes in gene transcription of Salmonella Typhimurium were investigated. Recovery of the heat-injured S. Typhimurium cells in Tryptis Soy Broth (TSB) resulted in full recovery after 3 h of incubation at 37?. DNA microarray analysis of 60-min recovering cells revealed an increase in the transcription of 141 genes. Among them, genes of known function involved to various degrees in the recovery were: genes involved in branched-chain amino acid (BCAA) transport (livJ, livH), cell envelope integrity (ddg), heat-shock response (cpxP, rrmJ), phage shock protein (pspA), ribosome modulation factor (rmf), and virulence (sseB) transcriptionalregul ation (rpoE, rpoH, rseA, rseB, rseC ). It was found that supplementation of TSB with BCAA resulted in enhanced recovery of injured cells compared to those recovered without BCAA.