Relationship between membrane permeabilization and sensitization of S. aureus to sodium chloride upon exposure to Pulsed Electric Fields

The suitability of NaCl-added selective media for the quantification of electroporated bacterial cells was evaluated using Staphylococcus aureus as a model microorganism. A very good correspondence was found between the percentage of cells unable to outgrow in media added with the Maximum Non Inhibitory Concentration of NaCl and the percentage of electropermeabilized cells, as determined by propidium iodide staining and K+ release measurements. The relationship between the percentage of electropermeabilized cells and cells sensitized to NaCl was confirmed for different experimental conditions, such as cells in different growth phase, grown at different temperatures, or treated at different pHs and a. Among all the factors studied, only when cells were alkaline-shocked or treated at 10 degrees C, lack of correspondence between the percentage of electropermeabilized cells and those unable to outgrow in NaCl added media was found. Finally, the good correspondence between the number of electropermeabilized cells and those inhibited in NaCl-added media was also confirmed for other three bacterial species. Industrial relevance: Recovery in NaCl added media can be used for determining the number of electroporated bacterial cells generated by PEF treatments. This will help in Pulsed Electric Fields process optimization and PEF-based combined processes design. (C) 2015 Elsevier Ltd. All rights reserved.