Which is the best treatment for prosthetic joint infections due to Propioni- bacterium acnes: need for further biofi lm in vitro and experimental foreign- body in vivo studies?

We read with a great interest the recent paper by Jacobs et al. (2015) concerning the treatment of prosthetic joint infections (PJI) caused by Propionibacterium acnes and the associated comments (Bayston and Ashraf 2016). The fi rst paper suggests that combination therapy with rifampicin is not more effective than therapy without rifampicin. We dem- onstrated previously in vitro and in an animal foreign body infection model that the minimal eradication biofi lm concen- tration (MBEC) was the lowest with rifampicin (16 mg/L) alone compared with penicillin G, daptomycin, ceftriaxone, levofl oxacin, vancomycin, and clindamycin (Furustrand et al. 2012). However, we have reported the emergence of rifampicin-resistant P. acnes strains in vitro (Furustrand et al.