Objective: To determine whether Propionibacterium acnes is able to adhere to implant materials, and to develop biofilms.

Background: Most orthopaedic implant infections are caused by staphylococci, which express adhesins and can adhere to biomaterials and to plasma glycoprotein conditioning films. They then produce exopolymers and develop biofioms. P acnes, being anaerobic, is often missed as a cause of implant infection and might be more common than is realised, yet little is known about its virulence factors (ability to adhere to biomaterials or conditioning film and biofilm development).

Materials & Methods: Surgical steel or silicone coupons, with and without plasma conditioning film, were exposed to three clinical isolates of P acnes and examined by cultural methods and chemiluminescence for adherence. In further experiments, the coupons were incubated anaerobically with the P acnes strains for several days. They were then rinsed, fixed and processed for scanning electron microscopy (SEM). In a third set of experiments, coupons were again incubated anaerobically with P acnes and examined by laser confocal microscopy (LCM) for biofilm development.

Results: All three isolates of P acnes were able to adhere to the biomaterials, to a degree similar to that of a clinical isolate of Staphylococcus aureus, though not as strongly as Staphylococcus epidermidis. Unlike with the staphylococci, the presence of a conditioning film did not make a significant difference. SEM and LCM revealed biofilm development morphologically similar to that seen with S epidermidis. Exopolymer production was also demonstrated.

Conclusions: P acnes is able to adhere to biomaterials but not so avidly as S epidermidis. The adherence is not enhanced by plasma conditioning film. However, once adhered, P acnes is capable of developing a biofilm morphologically indistinguishable from that of S epidermidis. This probably explains the role of P acnes in implant infection, and the therapeutic difficulty it often poses.