Mode of action of hydrogen peroxide and other oxidizing agents: differences between liquid and gas forms

Antimicrobials such as chlorine dioxide, peracetic acid and hydrogen peroxide (H2O2) share a basic mechanism of action (chemical oxidation of cellular components), but profound differences arise in their efficacy against microorganisms. Optimization of activity requires an understanding of their interaction with microbial targets and a clear differentiation between the chemical efficacies of each oxidative biocide. This study aimed to elucidate the biochemical mechanisms of action of oxidizing biocides at a macromolecular level, using amino acids, protein and an enzyme as model substrates for the action of each biocide. The interactions of a number of oxidising agents (liquid and gaseous H2O2, ClO2, peracetic acid formulations) with amino acids, proteins (bovine serum albumin and aldolase) and enzymes were investigated by spectrophotometry, SDS-PAGE and alkaline phosphatase activity measurements. Biocide reactions yielded different types of oxidative structural change and different degrees of oxidation to amino acids and proteins, and differences in activity against a microbial enzyme. In particular there was a marked difference in the interactions of liquid H2O2 and gaseous H2O2 with the macromolecules, the latter causing greater oxidation; these results explain the dramatic differences in antimicrobial efficacy between liquid and gas peroxide. These results provide a comprehensive understanding of the differences in interactions between a number of oxidizing agents and macromolecules commonly found in microbial cells. Biochemical mechanistic differences between these oxidative biocides do exist and lead to differential effects on macromolecules. This in turn could provide an explanation as to their differences in biocidal activity, particularly between liquid and gas peroxide.