title: Influence of Co-Cr particles and Co-Cr ions on the growth of staphylococcal biofilms.
abstract: OBJECTIVE
  In the last decades, hip prostheses with a metal-on-metal (MOM) bearing have been implanted by orthopedic surgeons worldwide. However, concerns are now raised towards the metal particles and degradation products released by MOM-bearings into surrounding tissue, although effects of Co-Cr wear on infection are also unknown. Therefore, we here determine the viable volumes of staphylococcal biofilms formed on polystyrene in the absence and presence of Co-Cr particles and Co-Cr ions.
  
  
  METHODS
  Three clinically derived and two commercially available staphylococcal strains were grown in the presence of 2 mg/mL Co-Cr particles or 1000/500 µg/L Co-Cr ions derived from Co-Cr salts or from particle supernatant, under static and dynamic growth conditions. A dynamic model simulates the conditions that apply for biofilm formation in the human body, as synovial fluid in mobile patients with hip prostheses is in constant motion with accompanying shear rates. Images of 24 h old biofilms were made with confocal laser scanning microscopy and analyzed with the mathematical computer program COMSTAT, yielding the biovolume of a biofilm. X-ray photoelectron spectroscopy was performed on the particles to study their elemental surface composition.
  
  
  RESULTS
  Most isolates showed a tendency of reduced biofilm growth in the presence of Co-Cr particles compared to growth during exposure to metal ions, but this was only significant in one strain under the dynamic growth condition (Staphylococcus aureus 7388). Characterization of the outer surface of the particles revealed a Co-Cr oxide layer enriched by Mo relative to the bulk concentration.
  
  
  CONCLUSIONS
  MOM bearings produce metal particles which were found to possess antibacterial characteristics under dynamic growth conditions. Further research is needed towards the clinical relevance of this finding.
authors.affiliation: Department of Biomedical Engineering, University Medical Center Groningen and University of Groningen, Groningen, The Netherlands.
authors.forename: Anton H
authors.initials: AH
authors.lastname: Hosman
authors.forename: Henny C
authors.initials: HC
authors.lastname: van der Mei
authors.forename: Sjoerd K
authors.initials: SK
authors.lastname: Bulstra
authors.forename: Roel
authors.initials: R
authors.lastname: Kuijer
authors.forename: Henk J
authors.initials: HJ
authors.lastname: Busscher
authors.forename: Daniëlle
authors.initials: D
authors.lastname: Neut
mesh_terms: D018441:Biofilms / Q000187:drug effects* / Q000254:growth & development; D002858:Chromium Alloys / Q000737:chemistry / Q000494:pharmacology*; D006622:Hip Prosthesis / Q000009:adverse effects*; D006801:Humans; D050296:Microbial Viability / Q000187:drug effects; D018613:Microscopy, Confocal; D008855:Microscopy, Electron, Scanning; D010316:Particle Size; D056951:Photoelectron Spectroscopy; D011474:Prosthesis Design; D016459:Prosthesis-Related Infections / Q000382:microbiology / Q000517:prevention & control*; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000254:growth & development; D013212:Staphylococcus epidermidis / Q000187:drug effects* / Q000254:growth & development; D013314:Stress, Mechanical; D013499:Surface Properties
chemical_list: D002858:Chromium Alloys