Bactericidal Activity of Superoxide Anion and of Hydrogen Peroxide: Investigations Employing Dialuric Acid, a Superoxide-Generating Drug

Abstract

The addition of dialuric acid (a superoxide-generating drug) to a suspension of resting human neutrophils resulted in a stimulation of cellular hexose monophosphate shunt activity. Measurement of oxygen consumption demonstrated a rapid rate of oxygen uptake by the drug alone in aqueous solution. The subsequent addition of catalase (but not of superoxide dismutase) resulted in a substantial release of oxygen, indicating that H ₂ O ₂ was accumulating in the media. The generation of O ₂ ⁻ by the drug was verified by measuring the rate of reduction of cytochrome c by the drug in the presence and absence of authentic superoxide dismutase. The growth of Escherichia coli B and Staphylococcus aureus was inhibited in vitro by addition of the drug to a suitable culture media; the degree of inhibition was dose dependent. This inhibition of bacterial growth could be completely reversed by the addition of as little as 5 μg of purified catalase, but was not affected by concentrations of superoxide dismutase that were 2,000-fold higher. These results suggest that the dialuric acid-induced stimulation of hexose monophosphate shunt activity in neutrophils is due to accumulated H ₂ O ₂ . Further, the contribution of superoxide to the bactericidal activity towards E. coli and S. aureus is probably minimal compared with that of H ₂ O ₂ .