The association of dextran sodium sulfate to the bioactive agent I-modulia® attenuates Staphylococcus aureus virulence expression and δ-toxin production

As a part of the human skin commensal bacterial community, Staphylococcus aureus contributes to the host's immune system education. Nevertheless, it is also considered as an opportunistic pathogen involved in cutaneous infections or skin pathologies, in particular atopic dermatitis. To switch to a pathogenic behavior, S. aureus uses regulatory mechanisms to collectively produce virulence factors. Deprivation of these factors has emerged as a promising way to prevent or treat Staphylococcal diseases in facilitating the role of the immune system, while preserving the protective one of the commensal communities. This study focuses on the anti-virulent effect of dextran sodium sulfate (DSS) and I-modulia®, two natural products that have already proven their value in skincare. The anti-virulent capacity of DSS was first demonstrated by a dose-dependent inhibition of δ-toxin release, a virulence factor known to be a potent inducer of mast cell degranulation, on in vitro S. aureus cultures at high and low virulent states. A transcriptomic study was then implemented for a comprehensive overview of the anti-virulent impact. The results have shown the downregulation of many transcripts related to host immune evasion (scn, sbi), as well as exotoxins (α,γ-toxin) and adhesins production (map, emp), mostly under the control of SaeRS Two-Component System (TCS), one of the two major virulence regulators in S. aureus. Interestingly, genes related to secretion systems and the synthesis of exo-proteases were significantly downregulated when DSS was used in combination with I-modulia®. The repression of these genes was not previously observed and reflects a broader inhibitory action. We have also demonstrated that the inhibition of virulence factors didn't affect S. aureus viability. Our findings suggest that combining DSS and I-modulia® could be a promising therapeutic strategy to counteract microbial dysbiosis in the treatment of S. aureus skin pathologies in re-empowering the host's natural immune defenses.

Effect of a low-mineralized thermal spring water on skin barrier mechanical properties using atomic force microscopy

The mineral content of thermal spring water (TSW) applied to the skin surface can directly influence the skin barrier. Indeed, our previous study showed that Avène TSW (ATSW), a low mineral content thermal spring water, protects the stratum corneum from dehydration compared to a mineral-rich TSW (MR-TSW) and maintains skin surface ultrastructure. While many TSWs have been recognized to have beneficial effects on skin, little is known about their localized and specific effects on skin barrier biomechanics at the nanometric scale. The aim of this study was to compare the effects of ATSW with a reference, MR-TSW, on the biomechanical barrier properties of the skin under homeostasis conditions using atomic force microscopy (AFM). AFM was used to obtain a precise nanomechanical mapping of the skin surface after three applications of both TSW. This provides specific information on the skin topographical profile and elasticity. The topographic profile of skin samples showed a specific compaction of the skin layers after application of MR-TSW, characterized by an increase of the total number of external skin layers, compared to non-treated samples. By contrast, ATSW did not modify the skin topographic profile. High-resolution force/volume acquisitions to capture the elastic modulus showed that it was directly correlated with skin rigidity. The elastic modulus strongly and significantly increased after MR-TSW application compared to non-treated skin. By contrast, applications of ATSW did not increase elastic modulus. These data demonstrate that applications of MR-TSW significantly modified skin barrier properties by increasing skin surface layer compaction and skin rigidity. By contrast, ATSW did not modify the topographical profile of skin explants nor induce mechanical stress at the level of the stratum corneum, indicating it does not disrupt the biophysical properties linked to skin surface integrity.