Salmonella enterica Senftenberg (IOC 2319) and Salmonella enterica Typhimurium (ATCC 14028) under low water activity stress: Effects on culturability and cell viability

Salmonella enterica is one of the most important foodborne pathogens for public health worldwide. When Salmonella enterica is exposed to low water activity, changes in cellular behavior may occur. These changes can impact the cells that form a colony on specific nutrient media (culturability) and the metabolically or physiologically active cells (viability) of Salmonella cells, with consequences for the analytical methods and food safety management. Thus, this study studied the impact of continuous and recurrent exposure of S. Senftenberg IOC 2319 and S. Typhimurium ATCC 14028 to water activity (a_w) treatments between 0.4 and 0.99 over 24 h and five days. The culturability was determined using the plate count technique, and cell viability was measured by flow cytometry. S. Senftenberg IOC 2319 was shown to be more resistant to a_w stress than S. Typhimurium ATCC 14028. A total of 6.9 and 8.5 log CFU/mL reductions were observed for S. Senftenberg IOC 2319 and S. Typhimurium ATCC 14028. Although both bacteria lost culturability on plate counting, the flow cytometry results demonstrated that they remained viable between 7.09 and 9.23 log CFU/mL for S. Senftenberg IOC 2319 and S. Typhimurium ATCC 14028, respectively. This result opens questions about whether they can recover and adapt a food matrix, causing a greater risk to the consumer. In conclusion, low water activity stresses can cause significant changes in Salmonella strains, and the use of Flow cytometry can be a valuable technique to understand the physiological status of microorganisms better and suggest the importance of safer and faster methods for standard microbiological evaluation.