Effect of slightly acidic electrolyzed water for inactivating Escherichia coli O157:H7 and Staphylococcus aureus analyzed by transmission electron microscopy

The use of different available chlorine concentrations (ACCs) of slightly acidic electrolyzed water (SAEW; 0.5 to 30 mg/liter), different treatment times, and different temperatures for inactivating Escherichia coli O157:H7 and Staphylococcus aureus was evaluated. The morphology of both pathogens also was analyzed with transmission electron microscopy. A 3-min treatment with SAEW (pH 6.0 to 6.5) at ACCs of 2 mg/liter for E. coli O157:H7 and 8 mg/liter for S. aureus resulted in 100% inactivation of two cultures (7.92- to 8.75-log reduction) at 25°C. The bactericidal activity of SAEW was independent of the treatment time and temperature at a higher ACC (P > 0.05). E. coli O157:H7 was much more sensitive than S. aureus to SAEW. The morphological damage to E. coli O157:H7 cells by SAEW was significantly greater than that to S. aureus cells. At an ACC as high as 30 mg/liter, E. coli O157:H7 cells were damaged, but S. aureus cells retained their structure and no cell wall damage or shrinkage was observed. SAEW with a near neutral pH may be a promising disinfectant for inactivation of foodborne pathogens.