title: Antibiotic susceptibility of Propionibacterium acnes isolated from orthopaedic implant-associated infections.
abstract: BACKGROUND
  Prosthetic joint infections (PJIs) caused by Propionibacterium acnes account for a larger proportion of the total number of PJIs than previously assumed and thus knowledge of the antimicrobial susceptibility patterns of P. acnes is of great value in everyday clinical practice.
  
  
  METHODS
  Using Etest, the present study investigated the susceptibility of 55 clinical isolates of P. acnes, obtained from orthopaedic implant-associated infections of the knee joint (n = 5), hip joint (n = 17), and shoulder joint (n = 33), to eight antimicrobial agents: benzylpenicillin, clindamycin, metronidazole, fusidic acid, doxycycline, moxifloxacin, linezolid and rifampicin. Synergy testing was also conducted, in which rifampicin was combined with each of the remaining seven antibiotics.
  
  
  RESULTS
  All isolates (n = 55) were susceptible to most of the antibiotics tested, with the exception of 100% resistance to metronidazole, five (9.1%) isolates displaying decreased susceptibility to clindamycin, and one (1.8%) to moxifloxacin. None of the antimicrobial agents investigated were synergistic with each other when combined and nine isolates were antagonistic for various antimicrobial combinations. The majority of the antimicrobial combinations had an indifferent effect on the isolates of P. acnes. However, the combination of rifampicin and benzylpenicillin showed an additive effect on nearly half of the isolates.
  
  
  CONCLUSIONS
  Almost all P. acnes, isolated from orthopaedic implant-associated infections, predominantly PJIs, were susceptible to the antibiotics tested, with the exception of complete resistance to metronidazole. Synergy test could not demonstrate any synergistic effect but additive effects were found when combining various antibiotics. Antagonistic effects were rare.
authors.affiliation: Faculty of Medicine and Health, Örebro University, Örebro, Sweden; Department of Laboratory Medicine, Clinical Microbiology, Örebro University Hospital, Örebro, Sweden.
authors.forename: Jasmine
authors.initials: J
authors.lastname: Khassebaf
authors.affiliation: Department of Laboratory Medicine, Clinical Microbiology, Örebro University Hospital, Örebro, Sweden.
authors.forename: Bengt
authors.initials: B
authors.lastname: Hellmark
authors.affiliation: Faculty of Medicine and Health, Örebro University, Örebro, Sweden; Department of Urology, Örebro University Hospital, Örebro, Sweden.
authors.forename: Sabina
authors.initials: S
authors.lastname: Davidsson
authors.affiliation: Department of Laboratory Medicine, Clinical Microbiology, Örebro University Hospital, Örebro, Sweden.
authors.forename: Magnus
authors.initials: M
authors.lastname: Unemo
authors.affiliation: Division of Infectious Diseases, Department of Clinical and Experimental Medicine, Faculty of Health Sciences, Linköping University, Linköping, Sweden; Department of Infectious Diseases, County Council of Östergötland, Linköping, Sweden.
authors.forename: Åsa
authors.initials: Å
authors.lastname: Nilsdotter-Augustinsson
authors.affiliation: Faculty of Medicine and Health, Örebro University, Örebro, Sweden. Electronic address: bo.soderquist@orebroll.se.
authors.forename: Bo
authors.initials: B
authors.lastname: Söderquist
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D016908:Gram-Positive Bacterial Infections / Q000382:microbiology*; D006801:Humans; D008826:Microbial Sensitivity Tests; D058889:Molecular Typing; D019637:Orthopedic Procedures / Q000009:adverse effects*; D010802:Phylogeny; D011425:Propionibacterium acnes / Q000145:classification / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification*; D016459:Prosthesis-Related Infections / Q000382:microbiology*
chemical_list: D000900:Anti-Bacterial Agents
keywords: Antibiotic susceptibility testing; Etest; Propionibacterium acnes; Prosthetic joint infections; Synergy testing