Mechanisms of the bactericidal activity of low amperage electric current (DC)

The mechanisms whereby low amperage (10-100 microA) electric current (DC) is bactericidal were investigated with Staphylococcus epidermidis and Staphylococcus aureus. A zone of inhibition test involving the insertion of an anode and cathode into an agar plate inoculated with a lawn of bacteria was used to study the antimicrobial activity of electric current. A zone of inhibition was produced around the cathode when 10 microA (DC) was applied for 16 h. The diameter of the zone was greatly reduced in the presence of catalase. There was no zone around the cathode when the test was carried out under anaerobic conditions. H2O2 was produced at the cathode surface under aerobic conditions but not in the absence of oxygen. A salt-bridge apparatus was used to confirm that H2O2 was produced at the cathode and chlorine at the anode. The antimicrobial activity of low amperage electric current under anaerobic conditions and in the absence of chloride ions against bacteria attached to the surface of a current carrying electrode was also investigated. Antibacterial activity was reduced under anaerobic conditions, which is compatible with the role of H2O2 as a primary bactericidal agent of electricity associated with the cathode. A reduction in chloride ions did not significantly reduce the antibacterial activity suggesting that chlorine plays only a minor role in the bactericidal activity towards organisms attached to anodal electrode surfaces. The localized production of H2O2 and chlorine and the intrinsic activity due to electric current may offer a useful method for eradicating bacteria from catheter surfaces.