Removal Mechanism of Cutibacterium acnes Biofilms: A Comparison between Synthetic Surfactants and Rhamnolipid Biosurfactants.

Biofilms are composed of autogenously secreted extracellular polymeric substances (EPS) and affect nearly all aspects of human activity. Biofilms with negative health and economic effects can be controlled through the integrated use of surfactants and mechanical force. However, the relationships between the surfactant molecular structures and biofilm removal pathways have not been sufficiently elucidated. Additionally, Cutibacterium acnes (C. acnes), a skin commensal bacterium with biofilm-forming capabilities that can exacerbate acne vulgaris, has been rarely investigated. In this study, we established a shear flow system and employed a multianalytical framework integrating gravimetry, spectroscopy, thermodynamics, and microscopy to investigate the removal mechanisms of C. acnes biofilms by synthetic surfactants and biosurfactant rhamnolipids (RLs). Biofilm detachment from silica substrates was observed under turbulent flow in the presence of anionic surfactants, namely, sodium dodecyl sulfate (SDS) and RLs. By contrast, biofilms remained intact under static conditions. The detachment of biofilms from hydrophobic substrates independent of surfactant presence highlights that shear force and surfactant headgroup properties are the primary drivers in overcoming the robust biofilm-silica adhesion. Mechanistically, SDS disrupted and detached the biofilm structure upon shear application, driven by its high penetrative partitioning into the biofilm consisting of the EPS matrix and bacterial cells. Conversely, RLs facilitated efficient interfacial peeling from the silica surface via their carboxylate groups without structurally disrupting the biofilm. Our findings provide valuable insights for rational screening and formulation design of cleansing agents based on the physicochemical properties of biofilms.