Figure 1: Host cell type-specific internalization of Cutibacterium acnes.

(A) MG-63 cells were infected with different C. acnes strains at a MOI of 100:1 for 2 hours. After 2 h, cells were washed, treated with penicillin/streptomycin, washed again and lysed. CFU counts were determined after 5 days of anaerobic culture of the lysate on Schaedler plates. *P < 0.01. (B) MG-63 cells, osteoclasts (OC) and mesenchymal stem cells (MSC) were infected with different C. acnes strain at a MOI of 100:1 for 2 hours. After 2 h, cells were washed, treated with penicillin/streptomycin, washed again and lysed. CFU counts were determined after 5 days of anaerobic culture of the lysate on Schaedler plates. **P < 0.01. (C) MG-63 cells Gram stained (ATCC6919 C. acnes cells appear in purple). (D) Live confocal microscopy pictures after 2 h of incubation with MG-63 cells and washing. MG-63 cell membranes were stained with calcein red/orange (red). C. acnes bacteria were stained with fluorescein isothiocyanate (green). D1. Result with C. acnes ATCC6919 strain. D2. Result with C. acnes BL isolate. (E) Orthogonal views from different planes (x/y, x/z or y/z) of the live confocal microscopy images used to analyze the ATCC6919 CC18 C. acnes location. Bacteria (FITC, green) inside the cell (cellular membranes, stained with calcein red/orange, appear in red) are indicated by a white arrow.