Antimicrobial activity of gentamicin palmitate against high concentrations of Staphylococcus aureus

The reduction of implant related infections plays a pivotal role in orthopaedic surgery as an increasing number of people require implants (up to 200,000 per year in the United States (source: Joint Implant Surgery & Research Foundation 2010)). The aim of the current study is to prevent and thus decrease the number of bacterial infections. Both pre and post operative systemic antibiotic treatment and gentamicin containing bone cements (polymethylmethacrylate, PMMA) are commonly used strategies to overcome infections. In this study, the antimicrobial efficacy of gentamicin sulfate loaded bone cement was compared with titan discs coated with a new form of gentamicin, gentamicin palmitate. Adherence prevention, killing rates and killing kinetics were compared in an in vitro model, using Staphylococcus aureus (S. aureus), which together with Staphylococcus epidermidis (S. epidermidis) represents 60% of bacteria found responsible for hip implant infections (An and Friedman, 1996, J Hosp Infect 33(2):93-108). In our experiments gentamicin, which was applied as gentamicin palmitate on the surface of the implants, showed a high efficacy in eliminating bacteria. In contrast to gentamicin sulfate containing bone cements, gentamicin palmitate is released over a shorter period of time thus not inducing antibiotic resistance. Another benefit for clinical application is that it achieves high local levels of active ingredient which fight early infections and minimize toxic side effects. Furthermore, the short term hydrophobic effect of gentamicin palmitate can successfully impede biofilm formation. Thus, the use of self-adhesive antibiotic fatty acid complexes like gentamicin palmitate represents a new option for the anti-infective coating of cementless titan implants.