Bactericidal activity of manganese and iodide ions against Staphylococcus aureus: a possible treatment for acute atopic dermatitis.

We reported previously that balneotherapy using Kusatsu hot-spring water is useful for controlling the skin symptoms of acute flares/exacerbations of refractory cases of atopic dermatitis. As Staphylococcus aureus on the skin surface decreased in number or disappeared after balneotherapy, the hot-spring water was suspected to act against the microorganism. The hot-spring water showed strong bactericidal activity against S. aureus in vitro. In order to clarify the mechanism further, the bactericidal activity of the hot-spring water was examined by adding back cations and anions in same concentrations as those in the original hot-spring water, one at a time to cation- and anion-exchanged hot-spring water. The findings clearly demonstrated that the bactericidal activity was expressed by manganese and iodide ions in acidic conditions (pH 2.0-3.0). Thus, the probable mechanism for the improvement of skin manifestations through Kusatsu balneotherapy is the bactericidal activity of the hot-spring water against S. aureus. When added to water acidified with sulphuric acid (pH 2.0-3.0) a synergistic effect of the 2 ions was observed, so that an anti-staphylococcal effect was obtained even at low concentrations (1 mg/kg). Acidic solutions containing manganese and iodide ions may thus be clinically useful for treating skin conditions caused by S. aureus.