Evaluation of bactericidal activity of weakly acidic electrolyzed water (WAEW) against Vibrio vulnificus and Vibrio parahaemolyticus

Abstract

Vibrio parahaemolyticus and Vibrio vulnificus cause severe foodborne illness in humans; thus, to reduce outbreaks of disease, it is clearly important to reduce food contamination by these pathogens. Although electrolyzed oxidizing (EO) water has been reported to exhibit strong bactericidal activities against many pathogens, it has never been tested against V. vulnificus and V. parahaemolyticus. The purpose of this study was to evaluate the bactericidal activity of weakly acidic electrolyzed water (WAEW), a type of EO water, against V. vulnificus and V. parahaemolyticus. Cell suspensions and cell cultures of both pathogens were treated for 30 s with sodium hypochlorite solution containing 35 mg/L available chlorine concentration (ACC) or WAEW containing 35 mg/L ACC. After an initial inoculum of 5.7 log CFU/mL, the number of viable V. vulnificus cells was reduced by 2.2 logs after treatment for 60 s with sodium hypochlorite solution containing 35 mg/L ACC, while no cells survived treatment with WAEW for 30 s. Similar results were obtained for V. parahaemolyticus. Under open storage conditions, WAEW maintained bactericidal activities against cell suspensions of both strains after 5 weeks but disappeared against cell cultures of the two strains after 5 weeks. Under closed storage conditions, however, WAEW maintained bactericidal activities against both cell suspensions and cell cultures of each strain after 5 weeks. No cells were detected in the cell suspensions and cultures when the ACC of WAEW was more than 20 mg/L and treatment time was greater than 15 s. Bactericidal activity of WAEW against V. vulnificus cell culture was reduced when the ACC of WAEW was less than 15 mg/L but was maintained in the V. vulnificus cell suspension when the ACC of WAEW was 0.5 mg/L. Thus, the bactericidal activity of WAEW was primarily affected by ACC rather than treatment time. Similar results were obtained for V. parahaemolyticus, indicating that WAEW kills these microorganisms more quickly than a chemical product such as sodium hypochlorite (NaClO), even at equivalent ACCs.