Formation of sublethally injured Yersinia enterocolitica, Escherichia coli O157:H7, and Salmonella enterica serovar Enteritidis cells after neutral electrolyzed oxidizing water treatments

The impact of neutral electrolyzed oxidizing (NEO) water treatments on the formation of sublethally injured Yersinia enterocolitica, Escherichia coli O157:H7, and Salmonella enterica serovar Enteritidis cells was evaluated. When pathogens were treated with 6% NEO water, approximately 38% of the treated Yersinia population and 25% of the treated Salmonella population became sublethally injured. The highest sublethally injured population was found when Salmonella cultures were treated with 3% NEO water. Regardless of the NEO water concentration used, no sublethally injured E. coli O157:H7 cells were found. To evaluate the sensitivity of NEO water-treated cells, four additional stresses (heat treatment, pH, NaCl, and bile salt) were tested. NEO water treatments did not generate any cross protection of treated cells against the other stresses. The diluted NEO water treatments in combination with heat treatment at 51°C for 10 min led to the best synergistic antimicrobial effects with a combined reduction of 7 logs. The gene expression results showed that NEO water treatments led to the upregulation of ompR, ail, and ycfR. These genes are known for their involvement in cells' environmental stress responses. In summary, this study investigated the sublethal injury in pathogenic cells caused by NEO water treatments. Although sublethal injury was discovered, when combined with other mild stresses, the synergistic antimicrobial effects were able to further reduce the numbers of viable pathogenic cells. These results demonstrate the great application potential of NEO water as a nonthermal and less corrosive antimicrobial treatment.