Acne vulgaris is a common inflammatory disorder of the sebaceous follicles, affecting more than 80% of young adolescents that can also persist into adulthood. However, the mechanisms by which inflammatory lesions arise are poorly understood. Although, considerable evidences suggest that Propionibacterium acnes participates in the pathogenesis of acne vulgaris, the possible role of biofilm formation by P. acnes remains, as yet, to be elucidated. In the present study, we investigated the putative role of biofilm production by P. acnes in comedogenesis and in the progression towards inflamed acne lesions. The biofilm-forming ability of P. acnes strains was tested by a specific in vitro method, based on the clinical biofilm ring test (c-BRT). For each patient, we collected samples from healthy skin and from different type of acne lesions including microcomedon, comedon, papule and pustule in order to assess the presence of P. acnes. Microbial identification was performed using the VITEK®II automated system and by sequencing 16S rRNA gene.
Our results revealed that P. acnes strains were present in all the stages of acne progression, namely from the noninflamed microcomedon/comedon condition to the inflammatory phase characterized by papule/pustule. Nevertheless, a significantly higher number of P. acnes were isolated at both inflamed (papule and pustule) and noninflamed (comedon) acne lesions compared with microcomedon and healthy skin. Notably, all the strains analyzed were able to produce biofilm.
This study revealed that biofilm production by P. acnes is likely to participate in the development of both noninflamed and inflamed acne lesions by promoting bacterial persistence and thus contributing to the worsening and chronicity of the inflammatory disease.

Biofilms-producing Propionibacterium acnes attend at both inflamed and noninflamed acne lesions