Titanium nitride surfaces with silver concentrations of TiN/4.6at%Ag, TiN/10.8at%Ag and TiN/16.7at%Ag were produced using magnetron deposition. Antimicrobial and topographic properties affecting the interactions of the surfaces with microorganisms were assessed using Pseudomonas aeruginosa (1 mu m x 3 mu m rod-shaped Gram-negative bacteria) and Staphylococcus aureus (1 mu m coccus-shaped Gram-positive bacteria) with retention assays, live/dead staining, and strength of attachment measurements. Retention of P. aeruginosa on the surfaces increased with an increase in surface silver content, grain size and topography, but the cells were easily removed from the surface under water when a force was applied. S. aureus cells were retained in lower numbers, but once attached, cells were difficult to remove. S. aureus cells attached in increased numbers on surfaces with lower silver content and smaller dimension surface features. The modification of hard wearing surfaces by addition of silver increased the antimicrobial activity of the surface, but the spectrum of antimicrobial activity varied with the target cell and surface properties. This work demonstrates that a range of methods and cell types need to be tested against surfaces which either discourage cell colonization and/or are potentially antimicrobial since the novel surface properties produced may inadvertently select and give advantage to a particular cell species. This may, in turn, affect the predicted surface efficacy. (C) Koninklijke Brill NV, Leiden, 2011