Collateral adaptive responses induced by desiccation stress in Salmonella enterica

Some Salmonella enterica serovars adapt effectively to low-water activity (low-aw) environments but this desiccation stress also induces collateral responses that have not been fully explored. Additionally, it is not known how long these responses are retained during refrigerated storage of the dehydrated pathogen. To investigate these issues, two S. enterica serovars known to acquire desiccation resistance (Tennessee and Eimsbuettel) were studied. Incubating Salmonella in broth under dehydration stress for 72 h increased the biofilm-forming ability of serovar Tennessee but not Eimsbuettel. Both serovars entered a viable but nonculturable (VBNC) state in response to desiccation for 24 or 48 h. When desiccation-adapted cells were stored at 4 °C for 2 days, four desiccation-related genes, proV, STM1494, kdpA, and otsB, were significantly upregulated (>2-fold increase) and the universal stress response regulator, rpoS, was highly upregulated (>50-fold increase). When storage at 4 °C was extended to 14 days, the two serovars increased the expression of proV and rpoS genes. In contrast, the expression of two virulence regulatory genes, hilA and invA, was downregulated (>2-fold decrease) at both storage periods. In conclusion, desiccation-adaptation of Salmonella invoked multiple stress responses which could serve as targets for developing pathogen mitigation strategies in low-aw foods.