Characterization of Cutibacterium acnes isolated from prosthetic joint infections and healthy skin

Cutibacterium acnes is an anaerobic bacterium that contributes to the balance of the skin microbiota but is also responsible for prosthetic joint infections (PJIs). Phenotypic and genotypic characterization of C. acnes isolated from infected implants could identify specific traits associated with a higher risk of PJI. To address this hypothesis, the phenotypic and genotypic traits of 20 clinical isolates were analyzed and compared with those of seven strains isolated from the skin microbiota of healthy participants. In particular, the antibiotic susceptibility profile and the ability of bacteria to aggregate and form biofilms in vitro were investigated. In addition, the genomes of all isolates were sequenced to determine whether PJI-causing microorganisms share a distinctive phylogenetic profile. Antibiotic susceptibility, biofilm formation, and aggregate formation did not differ between commensal and pathogen isolates. By contrast, extracellular DNA was mostly present in clinical isolates compared with commensal C. acnes. Phylogenetic analysis failed to evidence differences between pathogens and commensal strains, while a phylogenetic distance was observed between sequence types. Results suggest that C. acnes isolated from PJIs and healthy skin share common phenotypic and genotypic traits, making them indistinguishable. Hence, further studies on the phenotypic and genotypic characteristics of C. acnes are needed, as the association between diverse phylotypes and diseases remains unclear and debated.