Hydrogen peroxide as a potent bacteriostatic antibiotic: Implications for host defense

Abstract

Host defense against bacterial pathogens in higher organisms is mediated in part by the generation of reactive oxygen species (ROS) by PMN. In this study, we determined the following effects of exposure of constant concentrations of H 2O 2 on E. coli in a culture continuously monitored for H 2O 2 concentration, numbers, and viabilities of cells: (1) E. coli growth rates monitored for 1 h were profoundly affected by concentrations of H 2O 2, between 25–50μM. (2) Complete bacteriostasis was observed at 100μM. (3) Significant cell killing was not observed until the concentration of H 2O 2 was greater than 500μM. (4) Bacteriostatic (25–50μM) concentrations of H 2O 2 appeared not to be toxic to human skin fibroblasts for a 2-h exposure. (4) Bacteriostasis by H 2O 2 could not be explained by metabolic inhibition, because intracellular ATP levels were not compromised at bacteriostatic doses of H 2O 2. (5) Measurements of H 2O 2 concentrations in subcutaneous abscess fluid infected with both E. coli and S. aureus indicated prevailing concentrations of the oxidant consistent with a proposed role of H 2O 2 in host defense.