4.  Propionibacterium acnes: An Emerging Pathogen in Biomaterial-Associated Infection

While it is generally accepted that Staphylococcus spp., including coagulase-negative staphylococci (CoNS), are associated with biomaterial-associated infection, it has become increasingly clear that Propionibacterium acnes is also a significant cause of such infections, especially in relation to prosthetic joint failure. P. acnes outnumbers CoNS in sebaceous gland-rich areas of the skin and has considerable pathogenic potential. Molecular phylogeny studies have revealed that P. acnes comprises major evolutionary lineages with distinct differences in the production of putative virulence determinants. Strains may, therefore, be benign skin commensals or have pathogenic and pro-inflammatory potential. The role of P. acnes in biofilm infections is often overlooked as, although P. acnes is microaerophilic-to-aerotolerant, for optimal isolation from clinical material, samples must be processed as for obligately anaerobic bacteria; biomaterials must be maintained in an anaerobic atmosphere immediately upon removal from the patient and adherent biofilm dislodged by mild ultrasound treatment. The application of non-culture methods does, however, overcome this problem and provides the potential to improve detection rates.