The skin is the human body’s largest organ and is occupied by a highly diverse microbiome. It is well established that certain species of probiotic bacteria confer health benefits to the human gut, such as epithelial repair, enhancement of the gut barrier and modulation of the immune response. However, recent research is starting to uncover potential benefits of probiotic bacteria and their extracts to influence skin health and disease. Previous work in our lab has shown that lysates of commensal bacteria, Lactobacillus rhamnosus GG (LGG), when applied to primary human keratinocytes enhance Tight Junctions and increase proliferation and migration of keratinocytes in scratch assays. However, no studies have investigated the efficacy and potential therapeutic benefits of topical LGG lysates on human skin. We hypothesised that bacterial lysate-induced crosstalk between the epidermis and dermis may influence expression of extracellular matrix components in the superficial dermis. Using healthy adult skin from donors (n=7) in an ex-vivo culture model, we show that topical application of LGG lysate modulates both epithelial and dermal compartments of human skin. Analysis of epithelial cell proliferation (Ki67) revealed a dose-dependent increase in percentage of cycling cells (from 2.2% up to 4.5%), coincident with morphological changes at the dermal-epidermal junction (DEJ). Immunofluorescence analyses of fibrillin-rich microfibrils (FRMs) in the papillary dermis (25 µm to DEJ) revealed a dose-dependent increase in fibrillin-1 expression (1.2 fold, P=0.02) and microfibril coverage (1.2 fold, P=0.05). Furthermore, we also detected a small but significant increase in elastic fibre coverage (Weigert’s resorcin-fuchsin stain; 1.3 fold, P=0.03) in the papillary dermis (50 µm to DEJ). Together these data indicate topical application of LGG lysate on human skin elicits changes in the dermal microfibril architecture which may therapeutically benefit skin biomechanics. Further work is required to elucidate the mechanisms underlying these effects.

Topical application of a bacterial lysate modulates changes to the fibrillin-rich microfibril network