A simple method for evaluating the antimicrobial capacity of insoluble powdered inorganic materials

Although several methods have been devised for determining the antimicrobial ability of various materials, they suffer from various limitations. For example, it is difficult to determine the antimicrobial ability of poorly water-soluble materials. This study proposes a simple method for evaluating the antimicrobial ability of insoluble powdered metal oxides based on the minimum inhibition concentrations (MICs) determined by combining the halo method, a common method for evaluating the antimicrobial ability, with the flat-plate dilution method. Using Al2O3 powder, which did not exhibit antimicrobial properties, as a diluent, we prepared a uniform mixture of Ag2O, CuO, and ZnO at several concentrations (ppm). We then tested the antimicrobial activity of these powders for antimicrobial activity against E. coli using the halo method. Our method can be highly useful in evaluating the antimicrobial ability of poorly water-soluble inorganic powdered materials.