Cutibacterium acnes and Staphylococcus epidermidis: the unmissable modulators of skin inflammatory response.

Acne is a multifactorial inflammatory dermatose that affects all age categories from teenagers to adults, resulting in important psychological impacts. Multiple hypotheses currently attempt to decrypt the physiopathology of this disease, and four main actors were identified as highly implicated in it: hyperkeratinization of the pilosebaceous follicle, hyperseborrheae, host factors (innate immunity) and skin microbiota. In this letter, we present results illustrating the impact of skin microbiota on inflammatory skin response, and how far the proper balance between each bacterial community, especially C. acnes and S. epidermidis, is crucial to maintain an appropriate inflammatory response on the skin. The data presented in this study demonstrate that within the skin microbiota, an imbalance between Cutibacterium acnes and Staphylococcus epidermidis, is able to induce the activation of inflammation-related markers such as IL-1ra, IL-6, IL-8, G-CSF and the molecules C5/C5a, soluble CD14 MIP-3beta, Serpin E1, VCAM-1 and beta-defensin-2. Moreover, S. epidermidis appears to have a more important role than C. acnes on the induction of inflammation-related markers, particularly on IL-6. This work is the basis of future in vitro studies to further understand acne physiopathology, inspiring the development of future innovative therapies based on skin microbiota modulation.