Acidified nitrite enhances hydrogen peroxide disinfection of Acanthamoeba, bacteria and fungi

In the human innate immune system, stimulated phagocytes release reactive nitrogen intermediates that can react with superoxide to form the powerful oxidant peroxynitrite and other less abundant species. In this study, the efficacy of hydrogen peroxide (H(2)O(2)) and acidified nitrite (NaNO(2)) alone and in combination was compared against a variety of bacteria, fungi and protozoa. Challenge test assays based on the international standard (ISO 14729) were used to determine the antimicrobial activity of H(2)O(2) and acidified NaNO(2) at pH 5 alone and in combination against Pseudomonas aeruginosa, Serratia marcescens, Staphylococcus aureus, Mycobacterium aurum, Bacillus subtilis spores, Candida albicans, Fusarium solani conidia and Acanthamoeba polyphaga trophozoites and cysts. When tested alone, both H(2)O(2) (0.4% v/v) and NaNO(2) (2 mg/mL, pH 5) produced a >= 4 log reduction in viability after 4 h of exposure for all bacteria and A. polyphaga trophozoites, but not B. subtilis spores, F. solani and A. polyphaga cysts, which gave a < 1 log kill after 6 h, and M. aurum, which gave a < 1 log kill with NaNO(2) only. However, the combination of H(2)O(2) and NaNO(2) resulted in a >= 4 log kill of all test organisms within 1 h. Addition of NaNO(2) also enhanced the antimicrobial efficacy of a H(2)O(2)-based contact lens disinfection system. The findings of this study demonstrate that acidified NaNO(2) can significantly enhance the antimicrobial activity of H(2)O(2) probably through the generation of peroxynitrite. The addition of acidified nitrite to 3% (v/v) H(2)O(2) solution may represent an improved one-step method for the disinfection of contact lenses, especially against highly resistant cysts of Acanthamoeba spp.