Antibiotic-loaded synthetic calcium sulfate beads for prevention of bacterial colonization and biofilm formation in periprosthetic infections

Periprosthetic infection (PI) causes significant morbidity and mortality in fixation and joint arthroplasty and has been extensively linked to the formation of bacterial biofilms. Poly(methyl methacrylate) (PMMA) cement or beads are commonly used for antibiotic release to the site of infection but display variable elution kinetics and also represent a potential nidus for infection, therefore requiring surgical removal. Absorbable cements have shown improved elution of a wider range of antibiotics and, crucially, complete biodegradation but limited data exist as to their antimicrobial and antibiofilm efficacy. Synthetic calcium sulfate beads loaded with tobramycin, vancomycin and a vancomycin & tobramycin dual treatment (1:0.24 w/w ratio) were assessed for their ability to eradicate planktonic methicillin resistant S. aureus (MRSA) and S. epidermidis, relative to PMMA beads. The ability of the beads to prevent biofilm formation over multiple days and eradicate preformed biofilms was studied using a combination of viable cell counts, confocal microscopy and scanning electron microscopy of the bead surface. Biofilm bacteria displayed a greater tolerance to the antibiotics than their planktonic counterparts. Antibiotic-loaded beads were able to kill planktonic cultures of 106 CFU/mL, prevent bacterial colonisation and significantly reduce biofilm formation over multiple days. However, established biofilms were harder to eradicate. This data further demonstrates the difficulty in clearing established biofilms and therefore early preventative measures are key to reducing the risk of PI. Synthetic calcium sulfate loaded with antibiotics has the potential to reduce or eliminate biofilm formation on adjacent periprosthetic tissue and prosthesis material, and thus reduce rates of periprosthetic infection.