Biofilm formation by Propionibacterium acnes on biomaterials in vitro and in vivo: impact on diagnosis and treatment.

Propionibacterium acnes is found increasingly as a cause of delayed infection, usually involving implanted biomaterials. Despite susceptibility to common antibiotics, such infections are very difficult to treat and usually require surgical removal of the device. Three clinical isolates of P. acnes were assessed for ability to adhere to titanium, surgical steel and silicone, with and without a plasma conditioning film. After adherence, the biomaterials were then incubated for a further 6 days and examined for biofilm development. All three isolates adhered to all three biomaterials similarly. Importantly, we were able to demonstrate biofilm formation, including production of exopolymer similar in appearance to the polysaccharide intercellular adhesin of Staphylococcus epidermidis. A case summary also demonstrated failure to eradicate P. acnes infection in a hydrocephalus shunt after prolonged treatment. The removed shunt showed obvious biofilm formation, initially obscured by exopolymer when viewed by environmental scanning electron microscopy. Biofilm development by P. acnes explains the difficulties encountered in clinical management of such infections.