Cutibacterium acnes (formerly Propionibacterium acnes) isolated from prosthetic joint infections is less susceptible to oxacillin than to benzylpenicillin

Introduction: The frequency of prosthetic joint infections (PJIs) due to Cutibacterium acnes (formerly Propionibacterium acnes) is increasing, especially shoulder PJIs. The recommended antibiotic prophylaxis for hip and knee arthroplasties is beta-lactam antibiotics, predominantly cephalosporins. However, for example in Sweden, isoxazolyl-penicillin cloxacillin is used. No specific recommendations for shoulder arthroplasties are available. The aim of the present study was to determine the minimum inhibitory concentration (MIC) values for different antibiotics for C. acnes; and, more specifically, to compare the MIC values for benzylpenicillin and oxacillin. Materials and methods: Minimum inhibitory concentration (MIC) values for nine different antibiotic agents were obtained by gradient test (Etest) using strains of C. acnes (n= 57) isolated from PJIs from shoulders (n=31), hips (n=21), and knees (n=5). Results: All isolates had low MIC values for most of the tested antibiotic agents, and showed a wild type MIC distribution. The exception was clindamycin with 9% of the isolates displaying decreased susceptibility. The MIC values obtained for benzylpenicillin were significantly lower than the MIC values for isoxazolyl-penicillin (oxacillin). Conclusion: These in vitro results indicate that benzylpenicillin might be a more effective prophylactic treatment to prevent shoulder PJIs caused by C. acnes. However, further studies on the subject are needed, and the effectiveness of the prophylactic treatment should be evaluated using randomized controlled studies and/or register-based studies.