From adhesion to destruction: minocycline's dual action against Cutibacterium acnes biofilms.

Background: Cutibacterium acnes biofilms are frequently identified in acne lesions and on implant surfaces contributing to bacterial resistance and subsequent treatment failure. While minocycline, a broad-spectrum tetracycline antibiotic, is a conventional therapeutic agent for C. acnes infections, its efficacy against biofilms remains unclear.

Objective: This study employed an in vitro biofilm model to examine the effects of varying minocycline concentrations at different stages of biofilm formation.

Methods: Using our established in vitro model of C. acnes early- and later-stage biofilms, we exposed the biofilms to different minocycline concentrations. Morphological changes were assessed visually, biofilm viability was measured via XTT assay, biofilm biomass was quantified by crystal violet staining, and three-dimensional structural alterations were analyzed using confocal laser scanning microscopy (CLSM).

Results: A low minocycline concentration (0.25 mmol/L) inhibited biofilm formation by reducing bacterial adhesion, whereas a higher concentration (> 4.0 mmol/L) eradicated mature biofilms and eliminated embedded bacteria.

Conclusion: The study results demonstrate that minocycline effectively inhibits C. acnes biofilm formation, supporting our hypothesis regarding its inhibitory effects. Additionally, this study addresses a gap in existing research on minocycline's impact on bacterial biofilms. Our findings also provide a reference for investigating minocycline's effects on biofilms formed by other bacterial species. Future studies will focus on elucidating the molecular mechanisms underlying this phenomenon.