Abstract
Chronic wounds are a real public health problem. One of the main complications is the recurrent progress towards infection with an underlying risk of amputation. The difficulty of management lies in the presence of a polymicrobial biofilm at the wound bed. The objective of this thesis was to promote the development of the state-of-the-art of this important pathophysiology phenomenon of biofilm but also to promote new approaches for therapeutic treatment of chronic wounds to reduce risk of morbid infections. This doctoral work enabled: i) to perfect diagnostic tools by creating a new in vitro model mimicking the environment in which bacteria evolve at the level of chronic wounds; ii) to study behavior (virulence, fitness, genomics, morphology, early biofilm formation, expression of key genes for biofilm formation) of reference strains and clinical strains of Staphylococcus aureus (SA) and Pseudomonas aeruginosa (PA) isolated on a patient wound, based on short or long-term exposure to a conventional or a chronic wound like environment. The results showed that exposure under stressful environmental conditions reduced the virulence and fitness of the strains in favor of a biofilm-oriented behavior; iii) demonstrate the impact of multiple bacteria in an environment. This work has particularly highlighted the decrease of the pathogenicity and the evolution of the expression of some genes involved in the biofilm of SA strain when in contact with PA strain. iv) the development of a dynamic biofilm formation and confocal imaging technique allowing the visualization of a three-dimensional polymicrobial biofilm and the evaluation of antimicrobial molecules on each bacterial species composing the biofilm polymicrobial after an automatized mechanical debridement. The combination of our new chronic wound-like medium and the microfluidic biofilm formation and 3D visualization system of the polymicrobial biofilm represents powerful tools to improve the understanding of the interactions governing biofilms but also to evaluate the effectiveness of candidate molecules in chronic wounds management.Key words: Chronic wounds, infections, biofilms, bacterial cooperation