Mechanisms of survival, responses and sources of Salmonella in low-moisture environments

Abstract

Some Enterobacteriaceae possess the ability to survive in low-moisture environments for extended periods of time. Many of the reported food-borne outbreaks associated with low-moisture foods involve Salmonella contamination. The control of Salmonella in low-moisture foods and their production environments represents a significant challenge for all food manufacturers. This review summarizes the current state of knowledge with respect to Salmonella survival in intermediate- and low-moisture food matrices and their production environments. The mechanisms utilized by this bacterium to ensure their survival in these dry conditions remain to be fully elucidated, however, in depth transcriptomic data is now beginning to emerge regarding this observation. Earlier research work described the effect(s) that low-moisture can exert on the long-term persistence and heat tolerance of Salmonella, however, data are also now available highlighting the potential cross-tolerance to other stressors including commonly used microbicidal agents. Sources and potential control measures to reduce the risk of contamination will be explored. By extending our understanding of these geno- and phenotypes, we may be able to exploit them to improve food safety and protect public health.

Keywords: Salmonella; adaptation; low-moisture; phenotypes; survival.

FIGURE 1

Summary of proposed responses occurring upon transition of a bacterial cell into a low-moisture environment. These include K⁺ uptake by the Kdp transporter, osmoprotectant transport (ProU, ProP, and OsmU), glutamate synthesis and trehalose biosynthesis. The up-regulation of fatty acid catabolism, Fe–S clusters formation and filament formation have also been observed, as well as an up-regulation of the RpoE and RpoS regulators. An increase in the number of OmpC porins in reduced moisture has also been observed. Finally there may be a possible role for cellulose and curli fimbriae in survival.