Host Response of Human Epidermis to Methicillin-Resistant Staphylococcus aureus Biofilm Infection and Synthetic Antibiofilm Peptide Treatment

Abstract

Bacterial biofilm infections associated with wounded skin are prevalent, recalcitrant, and in urgent need of treatments. Additionally, host responses in the skin to biofilm infections are not well understood. Here we employed a human organoid skin model to explore the transcriptomic changes of thermally-injured epidermis to methicillin-resistant Staphylococcus aureus (MRSA) biofilm colonization. MRSA biofilm impaired skin barrier function, enhanced extracellular matrix remodelling, elicited inflammatory responses including IL-17, IL-12 family and IL-6 family interleukin signalling, and modulated skin metabolism. Synthetic antibiofilm peptide DJK-5 effectively diminished MRSA biofilm and associated skin inflammation in wounded human ex vivo skin. In the epidermis, DJK-5 shifted the overall skin transcriptome towards homeostasis including modulating the biofilm induced inflammatory response, promoting the skin DNA repair function, and downregulating MRSA invasion of thermally damaged skin. These data clarified the underlying immunopathogenesis of biofilm infections and revealed the intrinsic promise of synthetic peptides in reducing inflammation and biofilm infections.

Keywords: DNA repair; RNA-Seq transcriptomic analysis; biofilm immunopathogenesis; extracellular matrix remodeling; host defense peptide; human skin; inflammation; innate immune response; skin barrier function.

Figure 1

Antibiofilm activity of DJK-5 in the human burned skin MRSA biofilm model. Human surplus skin obtained post-breast reduction surgery was thermally challenged at 150 °C for 10 s and cultured at the air–liquid interface. Two million MRSA (USA300-LAC) were spotted on top of the burned skin and cultured for 24 h, followed by 4 h topical peptide treatment [0.1% (5 µg) or 0.4% (20 µg) DJK-5 or fusidic acid]. Skin cross sections were visualized by H&E staining (a–d). The colony count recovered from each skin sample was determined (e). Statistical significance comparing peptide treated skins to MRSA control was performed using the Kruskal–Wallis test, Dunn’s multiple comparisons test. Geometric mean of colony-count from 3 donors (7–9 replicates per conditions) was indicated. The concentrations of IL-1β (f), IL-6 (g), and IL-8 (h) in the skin culture medium was determined by ELISA. Error bars indicate mean with standard error in (f–h). Statistical significance of 5 replicates per condition from 3 donors was performed using one-way ANOVA, Dunnett’s multiple comparisons test (* p ≤ 0.05; ** p ≤ 0.01; *** p ≤ 0.001; **** p ≤ 0.0001).

Figure 2

NetworkAnalyst depiction of modulation of skin barrier function and extracellular matrix turnover by MRSA biofilm infection in thermally-injured skin. Minimum protein–protein interaction networks of cornified envelope formation (a) and extracellular matrix organization (b) comparing MRSA biofilm infected skin with burned skin control using NetworkAnalyst. Red nodes denote upregulation. Green nodes denote downregulation.

Figure 3

DJK-5 treatment downregulated IL-12 and IL-6 family interleukin responses in MRSA biofilm skin infection. Heatmaps of DE genes involved in the (a) IL-17, (b) IL-12 family (c), and IL-6 family signalling cascades in response to MRSA biofilm-induced skin inflammation with or without DJK-5 treatment. Color scale based on log₂fold-change of DE genes with red indicating upregulation and green indicating downregulation.

Figure 4

Network indicating DJK-5 enhancement of DNA repair functions in biofilm infected skin. A zero-order protein–protein interaction network of DE genes comparing DJK-5 treated vs. untreated MRSA biofilm skin infection using NetworkAnalyst. Red nodes denote upregulation.

Figure 5

DJK-5 downregulated MRSA invasion of thermally damaged N/TERT skin. Modified KEGG Pathview graph of extracellular matrix–receptor interactions and bacterial invasion of epithelial cells. Left half of each gene compares MRSA infected burned skin to burned skin control, and the right half of each gene compares DJK-5 treated to untreated MRSA infection of burned skin. Red indicates upregulation and green indicates downregulation.