Cutibacterium acnes Biofilm Study during Bone Cells Interaction

Abstract

Cutibacterium acnes is an opportunistic pathogen involved in Bone and Prosthesis Infections (BPIs). In this study, we observed the behavior of commensal and BPI C. acnes strains in the bone environment through bacterial internalization by osteoblast-like cells and biofilm formation. For the commensal strains, less than 1% of the bacteria were internalized; among them, about 32.7 ± 3.9% persisted intracellularly for up to 48 h. C. acnes infection seems to have no cytotoxic effect on bone cells as detected by LDH assay. Interestingly, commensal C. acnes showed a significant increase in biofilm formation after osteoblast-like internalization for 50% of the strains (2.8-fold increase). This phenomenon is exacerbated on a titanium support, a material used for medical devices. For the BPI clinical strains, we did not notice any increase in biofilm formation after internalization despite a similar internalization rate by the osteoblast-like cells. Furthermore, fluorescent staining revealed more live bacteria within the biofilm after osteoblast-like cell interaction, for all strains (BPIs and commensal). The genomic study did not reveal any link between their clinical origin and phylotype. In conclusion, we have shown for the first time the possible influence of internalization by osteoblast-like cells on commensal C. acnes.

Comparison of Two Cutibacterium acnes Biofilm Models

“…However, some strains, such as BPI 2 or BPI4, showed a very fine biofilm, with only a few aggregates. In our previous publication [ 38 ], we have observed that BPI biofilms were more important than commensal ones before internalization. In this case, our results were concordant.…”

“…This could be explained by the presence of large aggregates which could lead to bacteria death [ 39 ]. From a global point of view, the percentage of living bacteria within biofilm was higher in the dynamic than in the static model with the exception of C18 strains; with an average of 88.5% (±1%) for C2, C5, and C8 vs. an average of 56.8% (±9%) in the static model (data from reference [ 38 ]).…”

“…Based on our previous results [ 38 ], after testing seven commensal C. acnes strains, four were selected for their capacity to increase biofilm formation after their internalization in osteoblast-like cells to perform our experimentations. This change in their biofilm capacity served as a “landmark” element for comparison between static and dynamic models.…”

“…These data were compared to results previously obtained in a static model [ 38 ] to assess the modification of live/dead bacteria proportions after internalization in the two tested models. Even if the internalization of the four selected commensal strains (C2, C5, C8, and C18) had an impact in the biofilm formation through both models, the results clearly were in opposition.…”

“…This peculiar bacterial growth makes such chronic infections difficult to diagnose, to treat and to eradicate. In a previous study, several C. acnes strains were co-cultured with osteoblast-like cells in order to highlight the impact of the bacterial internalization into the host cells on the biofilm formation of C. acnes [ 38 ]. We used a static model in microtiter plates, in which biofilm biomass was stained with crystal violet or labelled with fluorochrome markers to quantify live and dead bacteria proportions.…”