In vitro and in vivo comparative colonization of Staphylococcus aureus and Staphylococcus epidermidis on orthopaedic implant materials.

Clinically, Staphylococcus aureus appears to be the dominant organism associated with infected metal implants, whereas coagulase-negative staphylococcal strains are more frequently isolated from infected polymer implants. We reproduced this trend experimentally in vitro and in vivo. Discs of a titanium alloy, poly(methyl methacrylate) and ultra-high molecular weight polyethylene were exposed to a clinical isolate of Staphylococcus aureus or either of two strains of Staphylococcus epidermidis. Within 1 h Staphylococcus aureus was always the most rapid colonizer regardless of biomaterial. However, after 8 to 24 h, Staphylococcus aureus was present in higher numbers on metal and Staphylococcus epidermidis on polymers. Moreover, the exopolysaccharide produced by Staphylococcus epidermidis appeared to offer an effective protection against host defences in vivo.