Cutibacterium acnes (formerly Propionibacterium acnes): friend or foe?

Cutibacterium acnes protects skin homeostasis. The species has three subspecies, and associations between C. acnes subsp. acnes and acne, C. acnes subsp. defendens and prostate cancer, and C. acnes subsp. elongatum and progressive macular hypomelanosis have recently been suggested. Different phylotypes/clonal complexes may cause prosthetic joint and other infections, and virulence factors such as fimbriae, biofilms, multidrug-resistance plasmids, porphyrin, Christie-Atkins-Munch-Petersen factors and cytotoxicity contribute to infections. Isolates are subtyped by multiplex PCR or multi- or single-locus sequence typing; however, these methods could be better synchronized. Resistance of acneic strains to macrolides (25.0-73.0%), clindamycin (10.0-59.0%) and tetracyclines (up to 37.0%) is worrisome, but susceptibility testing is now facilitated by European Committee on Antimicrobial Susceptibility Testing disk diffusion breakpoints. New therapeutic approaches include sarecycline, antimicrobial peptides and bacteriophages.