Propionibacterium acnes, an emerging pathogen: From acne to implant-infections

Propionibacterium acnes is a colonizer of the lipid-rich sebaceous glands of the skin. The pathogenicity of P. acnes has long been restricted to skin conditions. Its isolation from other anatomical sites or deep microbiological samples has often been considered as contamination. It is involved in the inflammation process of acne is well known, but until recently, it was neglected in other clinical presentations. P. acnes  has been considered to be of low virulence, but the new genomic, transcriptomic, and phylogenetic studies have allowed better understanding of this potential pathogen's importance in causing many chronic and recurrent infections, including orthopedic ( osteo-articular and spine )  and cardiac prosthetic, and breast or eye implant-infections, and neurosurgical infections of external ventricular shunts.

Hip Joint implant

These infections, are facilitated by the ability of P. acnes to produce a biofilm, requiring using anti-biofilm active antibiotics such as rifampicin. However, in the last 10 years, the rate of antibiotic-resistant bacteria has increased, especially for macrolides and tetracyclines. The antimicrobial susceptibility of P. acnes is not routinely performed in microbiology laboratories because of its susceptibility to a wide range of antibiotics.

Some antibiotics should be tested to adapt treatment because of the prevalence of antibiotic resistance in P. acnes: tetracycline, erythromycin, clindamycin, and cotrimoxazole. Furthermore, other antibiotics should be tested for severe infections, to optimize treatment and obtain a synergistic effect against P. acnes: penicillin, cephalosporins, vancomycin, quinolones, rifampicin, and the “new” antibiotics such as linezolid, daptomycin, and tigecycline, to which P. acnes is usually susceptible. Aminoglycosides and metronidazole are not active against P. acnes.

The treatment of severe infections caused by P. acnes includes a combination of antibiotics, administrated intravenously initially, and usually associated with optimal surgery (e.g., removal of the device and/or debridement of the surgical site). Penicillin G and ceftriaxone are still considered as first-line antibiotics for severe infections. Clindamycin, tetracycline, and levofloxacin are alternatives in those allergic to beta-lactams. Rifampicin and daptomycin are also active antimicrobial agents, effective also against P. acnes biofilm. Removal of the device associated with the infection is usually sufficient to reduce the inoculum causing chronic infection.

Gram stain of Propionibacterium acnes