Determination of Appropriate Sodium Chloride Concentration for Use in Preparation of Electrolyzed Acid Water with Disinfection Potential of Osmotic Pressure Taken into Account

The osmotic effect of sodium chloride (NaCl) used in the preparation of electrolyzed acid water (EAW) on the disinfection potential of EAW is elucidated in detail. Pseudomonas aeruginosa cells (109 CFU/mL) were brought into contact for 0–6 min with EAW (0.1), EAW (0.9), and EAW (1.8), which were prepared using 0.1%, 0.9%, and 1.8% NaCl solutions, respectively. EAW (0.9) had the tendency of the highest bactericidal potential, and they decreased the number of viable bacterial cells to less than 1/106 within 180s. To investigate the causes of variation in disinfection potential, morphological analysis by electron microscopy was performed. The number of blebs, through which the cytoplasm leaks out of the cell, was highest in cells exposed to EAW (0.1) followed by EAW (0.9), and EAW (1.8). The cytoplasm was most agglutinated in cells suspended in EAW (1.8). These results indicate that disinfection potential is determined by not only the pH or free residual chlorine concentration of EAW but also other physical properties related to the innate functions of bacterial cells, such as turgor pressure and plasmolysis. Therefore, it has been demonstrated that the osmotic pressure of the NaCl solution used for the preparation of EAW affects disinfection potential.