Understanding the iInteractions of hydrogen peroxide with macromolecules and microbial components

The bactericidal mechanism of hydrogen peroxide is poorly understood, with most evidence being obtained from studies involving greatly reduced concentrations aimed at investigating the effects of stress. Current theory suggests that this mechanism is based on the oxidation of protein, DNA and lipids within the cell by the production of free hydroxyl radicals through the interaction of hydrogen peroxide and intracellular iron. The mechanism of vapour phase hydrogen peroxide treatment remains unstudied, despite evidence that it may be different to the liquid phase. This study aimed to investigate the effects of bactericidal treatments of liquid and vapour phase hydrogen peroxide on the macromolecular components of a model organism, Escherichia coli strain K12. A set of treatment conditions producing a range of reductions in colony forming units was identified, and the effects of these conditions on the protein, DNA and lipid constituents of the cells assayed. No effect on the lipid contents and membrane integrity of treated cells was found. Liquid hydrogen peroxide was found to reduce the thiol content of cytoplasmic protein, but this was not found to be a major mechanism of bactericidal action. Extensive fragmentation of DNA was found to result by treatment with both phases, the degree of which was correlated with a reduction in colony forming unit counts. No effect on bactericidal action was found on addition of a hydroxyl radical scavenger or an inhibitor of protein synthesis, showing that DNA damage was due to the primary action of hydrogen peroxide, and that this damage was not caused by the production of free radicals within the cell. A modifed mechanism of hydrogen peroxide bactericidal action is proposed, whereby lethality is due solely to DNA damage caused by the production of ferryl radicals by the interaction of hydrogen peroxide and iron associated with the DNA backbone