Acrylic microparticles increase daptomycin intracellular and in vivo anti-biofilm activity against Staphylococcus aureus.

Daptomycin (DAP) is a cyclic lipopeptide antibiotic with potential clinical application in orthopedic infections caused by staphylococci. However, it failed to eradicate Staphylococcus aureus in vitro, in intracellular infection studies, as well as in vivo in an experimental model of implant-associated biofilm infections. In this study, the antimicrobial effect of DAP encapsulated in poly(methyl methacrylate)-Eudragit (PMMA-EUD) microparticles (DAP-MPs) on intracellular S. aureus was evaluated in human osteoblast cells using fluorescence in situ hybridization (FISH) analysis. Encapsulated DAP was able to reduce the amount of intracellular S. aureus by 73% compared to blank microparticles (MPs). Then, the advantage of treating with DAP-MPs versus free DAP was evaluated in a murine model of implant-associated biofilm infection. Free DAP showed a >3 log10 decrease in planktonic and adherent bacteria but failed to eradicate adherent methicillin-resistant S. aureus (MRSA), whereas DAP-MPs showed a clearance of planktonic MRSA, significantly reduced adherent MRSA by more than 3 log10 and cured the infection in 60%. This was linked to the prolonged higher DAP concentration within the tissue cage fluid compared to free DAP. To our knowledge, this study provides the first evidence for the high intracellular and in vivo anti-biofilm efficacy of DAP-MPs to target staphylococcal infections.