Background and Purpose: The remarkably low wear of metal-on-metal (MOM) bearings involving cobalt-chromium (Co-Cr) alloys has led to a resurgence in its use. However, consequences of these wear particles and the corrosion products are for the most part unclear. Recent research efforts towards the bacteriological influences of the MOM-degradation products suggested that particulate MOM debris promotes planktonic bacterial growth. On the other hand, extremely high concentrations of metal ions, derived from salts, have shown to possess bacteriostatic effects (growth reduction) on planktonic growth and on biofilm formation. The effects of salt-derived metal ions were found to be inhibitory and not bactericidal (lethal to bacteria). However, these two findings were both found under static growth conditions and no studies have investigated these findings under more clinically resembling dynamic growth conditions. In addition, influences of Co-Cr particles on biofilm formation have not yet been studied. Therefore, the aim of this study was to evaluate how Co-Cr particles and Co-Cr ions affect biofilm formation under static and dynamic growth conditions.
Methods: A collection of clinically isolated bacterial strains were exposed to Co-Cr particles and Co-Cr ions in concentrations as found in serum and above as found in adjacent tissue. The experiments were conducted as well under static, as under dynamic growth conditions. Biofilm formation in wells, stained with live/dead viability staining and visualized by confocal laser scanning microscopy, was analyzed with COMSTAT, yielding biovolume, biofilm thickness, and live/dead ratio of the bacteria within the biofilm.
Results: Co-Cr particle concentrations of 20 g/L reduced biofilm formation significantly. Moreover, these particle concentrations were found to be bactericidal (killed the bacteria). The live/dead ratio decreased when culturing was done under dynamic growth conditions when compared to the static growth condition. Under both growth conditions, biofilm formation was inhibited at concentrations of 10/5 mg/L Co-Cr ions, as reported to occur in synovial fluids. Co-Cr ion concentrations up to 1/0,5 mg/L revealed no consistent influence on biofilm formation.
Interpretation: Long-term clinical data on infection rates for Co-Cr MOM-bearings are not yet available, but the current results suggest that Co-Cr ions may yield these prostheses less prone to biofilm formation and subsequent infection.
