A role for Propionibacterium acnes in post-operative orthopedic implant infections

In the US annually there are 600,000 joint prostheses and 2,000,000 fracture-fixation devices surgically implanted with an average rate of infection of 2% and 5% respectively for primary insertion. [1]. Infected orthopedic hardware is most successfully cured by a combination of prolonged antibiotics and surgical replacement, sometimes involving a 2-step operative procedure that incurs increased cost and morbidity [1, 2]. Staphylococcus aureus and Coagulasenegative Staphylococcus (CoNS) account for about two thirds of these infections [1]. The difficulty in treating such infections has been attributed to biofilm formation and there is increasing evidence to support this hypothesis for Staphylococcal species infections. More recently Propionibacterium acnes has emerged as a possible pathogen in chronic hardware infections. Work from a group at The Queen’s University in Belfast has supported a role for the anaerobic, Gram-positive rod, Propionibacterium acnes, in “aseptic” prosthetic hip loosening [35]. They have proposed that P. acnes is an under recognized cause of chronic, low grade infection after prosthetic hip insertion and emphasized the need for better sampling of retrieved hardware along with strict anaerobic culturing techniques. Their work provides the best evidence that P. acnes exists in a biofilm on orthopedic implants. They have argued that P. acnes cannot simply be dismissed as a contaminant in operative samples even when a second, more recognized pathogen is identified.