Abstract
Chronic wounds, including Diabetic Foot Ulcers (DFU), affect mainly elderly and polypathological patients. In the context of an aging population, this will strengthen this problematic. Physiologically colonized by skin microbiota organized in a polymicrobial biofilm, these wounds host a network of interactions contributing to healing, stagnation, or exacerbation of the wound. The first article of the thesis is a literature review, describing the state of knowledge on microbial dynamics within chronic wounds and to sum up findings related to bacterial interactions within this niche. In previous work, our team focused on interactions between Staphylococcus aureus and Helcococcus kunzii, two bacteria frequently co isolated from DFU and showed potential interactions, with the commensal H. kunzii attenuating the virulence of the pathogen S. aureus.The aim of this thesis was to characterise the bacterial interactions occurring within chronic wounds and, more specifically, between commensals and pathogens in DFU, using the interaction between S. aureus and H. kunzii as a model.The first part of this thesis was focused on characterising the species H. kunzii at both the genomic and proteomic levels. Initially a genomic comparison of H. kunzii strains which show different abilities to modulate S. aureus virulence undertaken. This allowed us to identify proteins encoded by H. kunzii which could potentially modulate S. aureus virulence. The targets either harboured a motif common to auto-inducers of the S. aureus Agr system, a main regulator of S. aureus virulence, or an iron export system, iron being an essential cofactor of S. aureus virulence. We then used a proteomic approach to both validate production of these targets from a H. kunzii strain known to modulate the virulence of S. aureus and to study physiology of this commensal.In the second part, proteomic analysis allowed us to show that H. kunzii has not only an impact on the production of the regulator which controls the expression of staphylococcal virulence factors, but also a much wider effect on S. aureus metabolism. The effects on virulence transcriptional regulators were mediated by factors released into the medium by H. kunzii.Finally, we compared a panel of clinical co-isolates measuring growth, biofilm production and antibiotic resistance to evaluate the impact of this association.