Development of human skin models for the study of anti-bacterial adherence treatments

CD9 is a tetraspanin exploited by Staphylococcus aureus (S. aureus) in order to infect host cells. Thus, it has been identified as a target for anti-adhesion therapeutics that reduce contact between a pathogen and the host and thereby reduce infection. Furthermore, as anti-adhesion agents are not bactericidal, pathogenic resistance is less likely to occur in comparison to antibiotics. We have previously designed peptides targeting CD9 for anti-adhesion therapy and have successfully shown them to be effective in reducing S. aureus adherence to keratinocytes in 2D assays and 3D human skin models. However, the effects these peptides may have on immune cell function is currently unknown. The hypothesis of this study is that these peptides will be effective in reducing S. aureus infection in human skin without compromising immune cell function. Using a variety of models from 2D in vitro assays to 3D explants of human skin and to mouse models, we demonstrate that pre-treatment with CD9-derived peptides reduces S. aureus adherence to keratinocytes as shown by colony forming unit (CFU) counting, histology and flow cytometry. In addition, phagocytosis assays were performed with immune cells in isolation to show that peptide treatment did not negatively affect phagocytosis. In conclusion, we found that S. aureus infection is significantly reduced in skin models pre-treated with CD9 peptides in comparison to controls, and that immune cells pre-treated with peptides phagocytose the same amount of S. aureus as non-treated controls.