The oxidation based antimicrobial activity of silver is long known. Microparticles with a particular silver-ruthenium coating and specific physical properties were developed. The coating showed a considerably increased silver ion release rate in comparison to a plain silver coating. Accordingly, an exposure of Escherichia coli and Staphylococcus aureus to these silver-ruthenium coated microparticles resulted in a time and concentration dependent cell killing. Even though contact killing may contribute to this efficacy, rather a release associated diffusion gradient dependent killing was observed. Moreover, cell killing did not involve lysis. The coated microparticles manifested no reduction in antibacterial activity for months. Due to their specific size and density, they sedimented slowly in aqueous solution, showed a low aggregation tendency, and could be recycled easily. Hence, these silver-ruthenium coated microparticles lend themselves to a wide range of antibacterial applications as they combine long-term stability and high efficacy with ease of use.