Inactivation mechanism of ferrous and alkaline activated persulfate on Escherichia coli O157:H7 and Listeria monocytogenes

This study aimed to elucidate the mechanism of ferrous and alkaline activated persulfate in inactivating Escherichia coli O157:H7 and Listeria monocytogenes. A five-strain cocktail of each pathogen was treated with activated persulfate for 5 min. The treated pathogens were plated on both selective and non-selective agars. DNA and protein leakage, TTC-dehydrogenase relative activity, and cellular ultrastructure were analyzed. The results showed there were significant (P < 0.05) differences in colony counts between selective and non-selective agars for both pathogens after the activated persulfate treatment, indicating the presence of injured cells. The treated pathogens also showed significant leakages of intracellular DNA and protein content, indicating the cell envelope structures were damaged. The TTC-dehydrogenase relative activity of both pathogens was reduced to around 1% after 5 min treatment, indicating the key enzymes involved in cell metabolism were inhibited. Scanning and transmission electron microscopy imaging demonstrated both persulfate activation treatments caused significant damage on the cell walls and cell membranes. Cytoplasm agglutination and leakages were also observed. Based on the results, we proposed the inactivation mechanisms of ferrous and alkaline activated persulfate on pathogen cells are through breaking cell protective barriers, inhibiting key enzymes activities, and causing leakage of intracellular materials.