Propionibacterium avidum: a virulent pathogen causing hip periprosthetic joint infection

Background. Propionibacteria are important members of the human skin microbiota, but are also opportunistic pathogens associated with periprosthetic joint infections (PJI). While the role of Propionibacterium acnes in PJI has been widely described, insight into the capacity of Propionibacterium avidum to cause PJI is limited. Methods. An unusual cluster of four hip PJIs caused by P. avidum in one orthopedic center in 2015 prompted us to retrospectively identify and analyze clinical data related to previous P. avidum PJI cases (1997-2015). We also characterized the hemolytic and biofilm-producing capacity of our four clinical P. avidum strains isolated in 2015, and investigated their phylogenetic relationships by whole genome sequencing. Results. We retrospectively identified 13 P. avidum PJIs, with the majority being hip-related infections (n=11). Preoperative synovial fluid cultures were P. avidum positive in 63.6% of cases. Six out of 12 patients (50%) with available case histories were treated with an exchange of the prosthesis. In all but one of the six patients treated with debridement-retention of the prosthesis, treatment failed thus requiring a two-stage revision. The isolated P. avidum strains showed a more pronounced hemolytic activity, but a similar biofilm-forming ability when compared to P. acnes. Whole genome sequencing identified two phylogenetic clusters highly related to P. avidum PJI strains isolated in Sweden. Conclusions. We describe the largest series of P. avidum PJI predominantly located in the hip. Phylogenetic similarity of our P. avidum strains to PJI strains isolated elsewhere suggests these invasive lineages may be common.