Prosthetic Joint Infections (PJIs) are increasing with the use of orthopedic devices on an ageing population. Cutibacterium acnes is a commensal organism that plays an important role in the ecosystem healthy human skin, yet this species is also recognized as a pathogen in foreign body infection: endocarditis, prostatitis and specifically in PJIs. C. acnes is able to escape the immune system. This phenomenon could reflect two bacterial behaviour: the bacterial internalization by host cells and the biofilm formation. In this study, we studied different clinical strains of C. acnes. We noticed that C. acnes isolated from PJIs form 2 fold-more biofilm than the strains isolated from a normal skin in two models (Crystal violet staining and fluorescent microscopy (p=0.04 and p=0.02, respectively, Mann-Whitney test). We did not observe any difference in the internalization rate of those strains by osteoblasts. However, the quantity of biofilm formed by C. acnes before and after the internalization was compared. A significant increase in biofilm formation was observed for the strains isolated from the skin (x2.3±0.07; p=0.008, Mann-Whitney test). However, the hydrophobicity of the skin strains is significantly less important than for the PJIs strains (24.8±13% vs 56.6±12% respectively; p=0.003, Mann-Whitney test) but this did not change after internalization suggesting that there is no cell wall evolution. In conclusion, we studied for the first time the impact of bacterial internalization by osteoblasts on the virulent behaviour of C. acnes, which could explain the hided pathogenicity of this commensal bacterium.