Transmission Electron Microscopic Analysis Showing Structural Changes to Bacterial Cells Treated with Electrolyzed Water and an Acidic Sanitizer

Abstract

The effects of various sanitizers on the viability and cellular injury to structures of Escherichia coli and Listeria innocua were investigated. A food grade organic acidic formulation (pH 2.5) and acidic, neutral, and basic electrolyzed water [AEW (pH 2.7, oxidation reduction potential; ORP: 1100 mV, free available chlorine; FAC: 150 ppm), NEW (pH 6.9, ORP: 840 mV, FAC: 150 ppm), BEW (pH 11.6, ORP: -810 mV)] were used to treat E. coli and L. innocua cells. After 10 min of exposure to the sanitizers, changes to the bacterial numbers and cell structures were evaluated by plate counting and transmission electron microscopy (TEM), respectively. It was concluded from the results that the sanitizers reduced the E. coli cells between 2 and 3 log CFU/mL. Except for the BEW treatment, reductions in L. innocua population were greater (>1 log CFU/mL) than that of E. coli for all treatments. Data from the TEM showed that all sanitizers caused changes to the cell envelope and cytoplasm of both organisms. However, smaller changes were observed for L. innocua cells. Decrease in the integrity of the cell envelope and aggregation of the cytoplasmic components appeared to be mainly because of exposure to the sanitizers. The organic acid formulation and AEW were the most effective sanitizers against bacterial cells, indicating that penetration of acidic substances effectively caused the cell inactivation. An understanding of the method in which E-water and an acidic sanitizer cause injury to E. coli and L. innocua would be helpful in selecting an effective chemical agent as a food safety tool. This will allow a scientist to target similar microorganisms such as food borne bacteria with structures that are vulnerable to the sanitizer.