An assay to measure antibiotic efficacy against Staphylococcus epidermidis biofilms on implant surfaces.

Infection is a major limitation of implantable devices. Optimal antibiotic therapeutic regimes have not yet been defined. Implant-associated infections have a number of differentiating characteristics, which include the predominance of Staphylococcus epidermidis and other skin bacteria of normally low pathogenicity as the causative agents, together with a relative resistance to host defenses and to antibiotic therapy. These properties have been ascribed to the ability of the bacteria to exist on implant surfaces in the biofilm phase, which is protective. An assay of antibiotic activity using a standardized bacterial biofilm preparation of S. epidermidis is described. The assay is used to evaluate the relative efficacy of antibiotics to sterilize the biofilm, when they are used singly, or in double or triple combinations. The modulating effects of changing antibiotic concentrations and modifying the environment with CAPD variables (fresh and spent dialysis fluid, common PD solution additives) are also measured and the data summarized. It is hoped that, by using this and similar assays, individualized optimal therapeutic regimes of implant-associated infections may be logically planned.