Role of Rifampin against Propionibacterium acnes Biofilm In Vitro and in an Experimental Foreign-Body Infection Model

Propionibacterium acnes is an important cause of orthopedic-implant-associated infections, for which the optimal treatment has not yet been determined. We investigated the activity of rifampin, alone and in combination, against planktonic and biofilm P. acnes in vitro and in a foreign-body infection model. The MIC and the minimal bactericidal concentration (MBC) were 0.007 and 4 mu g/ml for rifampin, 1 and 4 mu g/ml for daptomycin, 1 and 8 mu g/ml for vancomycin, 1 and 2 mu g/ml for levofloxacin, 0.03 and 16 mu g/ml for penicillin G, 0.125 and 512 mu g/ml for clindamycin, and 0.25 and 32 mu g/ml for ceftriaxone. The P. acnes minimal biofilm eradication concentration (MBEC) was 16 mu g/ml for rifampin; 32 mu g/ml for penicillin G; 64 mu g/ml for daptomycin and ceftriaxone; and >= 128 mu g/ml for levofloxacin, vancomycin, and clindamycin. In the animal model, implants were infected by injection of 10(9) CFU P. acnes in cages. Antimicrobial activity on P. acnes was investigated in the cage fluid (planktonic form) and on explanted cages (biofilm form). The cure rates were 4% for daptomycin, 17% for vancomycin, 0% for levofloxacin, and 36% for rifampin. Rifampin cured 63% of the infected cages in combination with daptomycin, 46% with vancomycin, and 25% with levofloxacin. While all tested antimicrobials showed good activity against planktonic P. acnes, for eradication of biofilms, rifampin was needed. In combination with rifampin, daptomycin showed higher cure rates than with vancomycin in this foreign-body infection model.