The skin barrier comprises interdependent physical, chemical, immunological, and microbial components, of which the latter is constituted by a community of microbes residing on the skin surface that restricts the expansion of opportunistic pathogens, modulates keratinocyte signaling pathways, and fosters immune tolerance. However, molecular and cellular dynamics of host-microbe interactions remain incompletely characterized, partly due to the limited availability of physiologically relevant and robust preclinical models. We aimed to establish 3D human skin equivalents (HSEs) in co-culture with representative skin commensals to investigate host responses across an in vitro cohort of six biological replicates. Well-characterized HSEs were inoculated with Staphylococcus aureus, Staphylococcus epidermidis, and Cutibacterium acnes. A 48-hour co-culture period enabled microbial expansion, during which S. aureus exhibited the most substantial outgrowth, and strain-dependent variability was observed for S. epidermidis. Assessment of epidermal morphogenesis revealed that S. aureus exerted largest structural impact, whereas C. acnes promoted keratinocyte proliferation. Furthermore, S. aureus elicited a pro-inflammatory response, characterized by elevated secretion of IL-8 and CXCL1. In conclusion, we developed a reproducible experimental framework dissecting host-microbe interactions in HSEs to demonstrate that S. aureus induced substantial alterations in epidermal architecture and inflammatory signaling, underscoring its pathogenic potential in cutaneous environments.
Mieremet et al. (2026) studied this question.