Planktonic and Biofilm states of Staphylococcus aureus isolated from bone and joint infections and the in vitro effect of orally available antibiotics

Abstract Aims To demonstrate the in vitro activity of orally available antibiotics against Staphylococcus aureus isolated from bone or orthopedic implant materials. The biofilm eradication of the combination of three antibiotics was also assessed. Methods and results Clinical isolates from orthopedic infection samples were collected, and S. aureus isolates were classified according to their biofilm production and composition. Almost all S. aureus isolates (n = 36, 97.3%) produced biofilm and the major biofilm components were polysaccharides. Antimicrobial susceptibility was determined in planktonic (minimal inhibitory concentration; MIC) and biofilm cells (minimal biofilm eradication concentration; MBEC) using the MBEC Calgary Device. Overall, the MBEC ranged higher than the MIC. When combined at borderline-susceptible concentrations, moxifloxacin–rifampin and doxycycline–rifampin were both able to eradicate biofilms in a third of the strains whereas the doxycycline–moxifloxacin combination proved ineffective at eradicating biofilm, inhibiting it only in three strains. Conclusions We propose rifampin in combination with moxifloxacin or doxycycline for the design of clinical trials of bone and/or orthopedic device infection without proper debridement or material retention.