EVALUATION OF DAPTOMYCIN-SUPPLEMENTED ANTIBIOTIC-LOADED BONE CEMENT FOR TREATING VANCOMYCIN-RESISTANT ENTEROCOCCUS FAECALIS IN THE GALLERIA MELLONELLA IMPLANT INFECTION MODEL

Aim Periprosthetic infections caused by vancomycin-resistant pathogens, such as vancomycin-resistant Enterococcus faecalis (VRE), represent a major clinical challenge. Daptomycin can be incorporated into polymethyl methacrylate (PMMA) cement spacers. This study aimed to utilize the in vivo Galleria mellonella larvae implant infection model to determine the optimal dosage of daptomycin in different PMMA cements and evaluate its efficacy. Method Daptomycin (1 g or 2 g) was added to different PMMA cements (Cement 1 containing 1 g tobramycin; Cement 2 containing 0.5 g gentamicin), to produce bone cement implants. Control groups included non-loaded Cement 1 and Cement 2, as well as Reference 1 and Reference 2, without antibiotics. The test specimens were implanted into larvae of the greater wax moth ( G. mellonella ), followed by infection with 250 CFU of VRE DSM13591 after 1 hour. The survival of the larvae was monitored over time, and bacterial numbers in the larval tissue and on the implant surface were determined after 24h. These experiments were completed with in vitro proliferation assay and inhibition zone testing. Mechanical stability was measured according to ISO 5833 and DIN 53435. Results Survival and bacterial burden analysis demonstrated that the addition of 1 g or 2 g of daptomycin was effective in preventing VRE infections. There were significantly improved larval survival and reduced bacterial numbers in both the larval tissue and on the implant surface. In contrast, Cement 1 and Cement 2 alone did not enhance larval survival and showed outcomes comparable to the antibiotic-free control groups. The addition of daptomycin was found to be effective in inhibiting bacterial growth when compared to the references, with the largest inhibition observed for Cement 2 (2 g daptomycin). On day 42, sufficient bacterial growth inhibition was observed only with the addition of 2 g daptomycin. These results correlate with those from the proliferation assay. Adding more than 1.5 g daptomycin resulted in a reduction of mechanical strength, with Cement 1 no longer meeting the ISO standard for four-point bending strength. Conclusions The incorporation of daptomycin into ALBC successfully prevented VRE infections in an in vivo model. These findings emphasize the potential of the G. mellonella implant infection model as a valuable tool for evaluating the efficacy of ALBC against multidrug-resistant bacteria, thereby accelerating pre-clinical research and advancing strategies to combat PJI. We observed differences in mechanical stability and antimicrobial efficacy between daptomycin-loaded Simplex Tobramycin and Palacos R+G with increased stability and bacterial growth reduction for the latter one.