Prevention of Propionibacterium acnes biofilm formation in prosthetic infections in vitro

Abstract

Background: The role of Propionibacterium acnes in shoulder arthroplasty and broadly in orthopedic prosthetic infections has historically been underestimated, with biofilm formation identified as a key virulence factor attributed to invasive isolates. With an often indolent clinical course, P acnes infection can be difficult to detect and treat. This study investigates absorbable cements loaded with a broad-spectrum antibiotic combination as an effective preventive strategy to combat P acnes biofilms.

Methods: P acnes biofilm formation on an unloaded synthetic calcium sulfate (CaSO₄) bone void filler cement bead was evaluated by scanning electron microscopy over a period of 14 days. Beads loaded with tobramycin alone or vancomycin alone (as comparative controls) and beads loaded with a vancomycin-tobramycin dual treatment were assessed for their ability to eradicate planktonic P acnes, prevent biofilm formation, and eradicate preformed biofilms using a combination of viable-cell counts, confocal microscopy, and scanning electron microscopy.

Results: P acnes surface colonization and biofilm formation on unloaded CaSO₄ beads was slow. Beads loaded with antibiotics were able to kill planktonic cultures of 10⁶ colony-forming units/mL, prevent bacterial colonization, and significantly reduce biofilm formation over periods of weeks. Complete eradication of established biofilms was achieved with a contact time of 1 week.

Conclusions: This study demonstrates that antibiotic-loaded CaSO₄ beads may represent an effective antibacterial and antibiofilm strategy to combat prosthetic infections in which P acnes is involved.

Keywords: Propionibacterium acnes; antibiotics; biofilm; calcium sulfate; prosthetic infection; shoulder arthroplasty.