General response of Salmonella enterica serovar Typhimurium to desiccation: A new role for the virulence factors sopD and sseD in survival.

Salmonella can survive for long periods under extreme desiccation conditions. This stress response poses a risk for food safety, but relatively little is known about the molecular and cellular regulation of this adaptation mechanism. To determine the genetic components involved in Salmonella's cellular response to desiccation, we performed a global transcriptomic analysis comparing Salmonella Typhimurium cells equilibrated to low water activity (aw 0.11) and cells equilibrated to high water activity (aw 1.0). The analysis revealed that 719 genes were differentially regulated between the two conditions, of which 290 genes were up-regulated at aw 0.11. Most of these genes were involved in metabolic pathways, transporter regulation, DNA replication/repair, transcription and translation, and, more importantly, virulence genes. Overall design: S. Typhimurium cells were spotted on 0.2 µm polycarbonate filters and air dried for 24 hours at room temperature. Filters were then equilibrated for 4 days to two different water activitie: aw 1.0 as control condition, and aw 0.11 as low water activity and desiccating condition. Expression profile of cells equilibrated to low water activity (aw 0.11) was compared to the expression profile of cells in control conditions (aw 1.0).