Effects of Sucrose on Heat Resistance and Gene Expression in Salmonella Typhimurium

Increased foodborne outbreaks associated with low-moisture foods contaminated with Salmonella have raised the need for further insights into their possible causes and control measures. This study investigated the effects of sucrose-induced low water activity (aw) on heat resistance and global gene expression in Salmonella Typhimurium. Following heat treatment at 60 °C for 5 min, viable cell counts on TSA of the cells grown in TSB supplemented with 35% (w/v) sucrose for 24 h and resuspended in the same medium were 3-Log higher than those grown and resuspended in TSB without sucrose, and 1-Log higher than the cells grown in TSB and resuspended in TSB with 35% sucrose. Viability of the cells directly transferred from TSB to preheated TSB with sucrose was positively correlated with sucrose concentration. DNA microarray analysis identified sixteen up-regulated genes involved in cobalamin biosynthesis in the cells grown in the presence of 35% sucrose. Deletion of the pocR gene, which positively regulates cobalamin biosynthesis, resulted in suppression of the improvement in heat resistance of S. Typhimurium under sucrose-induced low aw, suggesting potential contribution of this gene in increasing heat resistance of S. Typhimurium.