gms | German Medical Science

Objectives: Multidrug-resistant (MDR) Gram-positive and Gram-negative bacterial strains belonging to the co-called ESKAPEE panel (i.e., Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Enterobacter species, plus Escherichia coli) represent a global threat to human health, because these bacterial strains can evade commonly used antibiotics. Implant-associated infections caused by MDR bacterial strains, especially due to increased resistance to aminoglycosides, are very difficult to treat. Here, we evaluate the effect of antibiotic-loaded bone cement (ALBC), containing several combinations of antibiotics, against ESKAPEE pathogens in vitro and in the Galleria mellonella implant infection model.

Methods: The commercially available bone cement containing 1 g of gentamicin and 1 g of clindamycin (COPAL G+C; Heraeus GmbH) was mixed with an additional 2 g of antibiotic (i.e., vancomycin (VAN), daptomycin (DAP), linezolid (LIN), meropenem (MER), or ciprofloxacin (CIP)), or with 10 MIU of colistin (COL), and made into discs and rod-shaped ALBC implants using a Teflon mold. These discs and rod-shaped ALBC implants were analyzed for their antimicrobial properties against a collection of ESKAPEE strains. To assess the in vitro bactericidal activity of the ALBC implants, surface microbicidal activity and agar diffusion assays were performed. Next, the antimicrobial activity of the ALBC implants was analyzed in the G. mellonella hematogenous implant infection model, where the bacteria were injected at 60 min after implantation. The larvae were kept at 37oC for five days after implantation and infection, and the survival was monitored. Moreover, the number of bacteria on the implant surface and in the peri-implant tissue was determined by sonicating the implant and homogenizing the tissue, respectively.

Results and conclusion: Adding DAP or VAN to COPAL G+C resulted in considerably lower number of MDR Staphylococcus aureus on the surface of the ALBC implants and in the surrounding tissue, when compared to Palacos R (i.e., without antibiotics) and COPAL G+C implants, enhancing the survival rate of the larvae. In case of MDR Enterococcus faecium, only the addition of DAP to COPAL G+C significantly decreased the number of bacteria on the surface of the ALBC implants and in the surrounding tissue and increased the survival of the larvae. In conclusion, addition of DAP to the clinically used Copal G+C bone cement is able to clear infections by MDR Gram-positive pathogens in the G. mellonella implant infection model.