Sporicidal activity of tertiary butyl hydroperoxide

Sporicidal action of peracetic acid and protective effects of transition metal ions

Although peracetic acid (PAA) is used widely for cold sterilization and disinfection, its mechanisms of sporicidal action are poorly understood. PAA at high concentrations (5-10%) can cause major loss of optical absorbance and microscopically-visible damage to bacterial spores. Spores killed by lower levels of PAA (0.02-0.05%) showed no visible damage and remained refractile. Treatment of spores of Bacillus megaterium ATCC 19213 with PAA at concentrations close to the lethal level sensitized the cells to subsequent heat killing. In addition, PAA was found to act in concert with hypochlorite and iodine to kill spores. Antioxidant sulfhydryl compounds or ascorbate protected spores against PAA killing. Trolox, a water-soluble form of alpha-tocopherol, was somewhat protective, while other antioxidants, including alpha-tocopherol, urate, bilirubin, ampicillin and ethanol were not protective. Chelators, including dipicolinate, were not protective, but transition metal ions, especially the reduced forms (Co2+, Cu+ and Fe2+) were highly protective. The net conclusions are that organic radicals formed from PAA are sporicidal and that they may act as reducing agents for spores that are normally in a highly oxidized state, in addition to their well known actions as oxidizing agents in causing damage to vegetative cells.

Microscopic and Thermal Characterization of Hydrogen Peroxide Killing and Lysis of Spores and Protection by Transition Metal Ions, Chelators, and Antioxidants

Killing of bacterial spores by H 2 O 2 at elevated but sublethal temperatures and neutral pH occurred without lysis. However, with prolonged exposure or higher concentrations of the agent, secondary lytic processes caused major damage successively to the coat, cortex, and protoplast, as evidenced by electron and phase contrast microscopy. These processes were also reflected in changes in differential scanning calorimetric profiles for H 2 O 2 -treated spores. Endothermic transitions in the profiles occurred at lower temperatures than usual as a result of H 2 O 2 damage. Thus, H 2 O 2 sensitized the cells to heat damage. Longer exposure to H 2 O 2 resulted in total disappearance of the transitions, indicative of major disruptions of cell structure. Spores but not vegetative cells were protected against the lethal action of H 2 O 2 by the transition metal cations Cu + , Cu 2+ , Co 2+ , Co 3+ , Fe 2+ , Fe 3+ , Mn 2+ , Ti 3+ , and Ti 4+ . The metal chelator EDTA was also somewhat protective, while o -phenanthroline, citrate, deferoxamine, and ethanehydroxydiphosphonate were only marginally so. Superoxide dismutase and a variety of other free-radical scavengers were not protective. In contrast, reducing agents such as sulfhydryl compounds and ascorbate at concentrations of 20 to 50 mM were highly protective. Decoating or demineralization of the spores had only minor effects. The marked dependence of H 2 O 2 sporicidal activity on moderately elevated temperature and the known low reactivity of H 2 O 2 itself suggest that radicals are involved in its killing action. However, the protective effects of a variety of oxidized or reduced transition metal ions indicate that H 2 O 2 killing of spores is markedly different from that of vegetative cells.