Influence of skin model cell-type composition on Streptococcus pyogenes infections

Necrotizing Soft Tissue Infections (NSTIs) are severe soft tissue infections that affect mostly skin, subcutaneous tissue and superficial fascia, and are characterized by presence of necrotic tissue. They are caused by different types of pathogens, but the most common agents belong to Group A Streptococcus (GAS). The majority of NSTI patients require intensive care and surgical intervention, with an associated mortality rate of 25-35%, up to 20% limbs amputation and 50% of risk to develop toxic shock. One characteristic of NSTI caused by GAS is that it often presents itself as a monomicrobial infection affecting the extremities of mostly healthy and young patients without underlying conditions. The underlying reasons that lead GAS NSTI infections to affect mainly peripheral body parts is not clear yet, however, the high concentration of thrombomodulin in plasma from patients with NSTI suggest a relevant role of the endothelium during infection. Thus in this thesis, we aim at elucidating the role of endothelial cells during infection with GAS. For this purpose, we established a protocol for integration of this cell type in an organotypic skin model, which was further used to characterize the infection process. The results show that endothelial cells can be efficiently integrated in the skin model, maintain anatomy and key organ functions. When the model is infected by GAS, tissue destruction and epithelial detachment is observed through immunofluorescence and histological stainings. The presence of endothelial cells promotes an higher bacterial load, possibly due to the cells themselves and not to secreted molecules. To sum up, we developed a 3D organotypic skin model with endothelial cells. The model can be used to study the pathogenesis of NSTI, host-pathogen interactions during infections and test antibiotic treatments.