Osteomyelitis or infection of bone is painful and difficult to treat due to limited tissue penetration by antibiotics. A resulting chronic infection has around a 30% chance of never resolving and resulting in amputation of the limb. The current standard of care for osteomyelitis is debridement and systemic antibiotics for two to six months, which can cause systemic toxicity and increase the emergence of antibiotic-resistant bacteria. It is therefore necessary to develop a localized biodegradable treatment that can deliver high concentrations of antimicrobials while minimizing the risk of systemic side effects. The overall objective of this work was to develop, characterize, and challenge locally delivered chitosan-based biomaterials loaded with either antibiotic or alternative antimicrobial agent(s) in either chronic or acute rat osteomyelitis models. The specific aims were to: (i) determine the chemical and biological interactions between chitosan hydrogels and fosfomycin in vitro, (ii) evaluate the antimicrobial efficacy of chitosan hydrogel loaded with fosfomycin antibiotic, either in the gel, in polylactic acid microparticles, or in both gel and microparticles in vitro and in a chronic rat osteomyelitis model, compared to blank chitosan hydrogel, and (iii) evaluate the antimicrobial efficacy of electrospun chitosan membranes loaded with cis-2-decenoic acid and/or bupivacaine in an acute rat osteomyelitis model, compared to current standard Celox™gauze. As hypothesized, chitosan biomaterials loaded with antimicrobial(s) reduced the bacterial burden and disease symptoms when compared to the standard treatment or blank materials. In closing, locally administrated antibiotics with prolonged availability via engineered biomaterials such as chitosan may allow for increased therapeutic efficacy against osteomyelitis.

Les chromogranines (Cgs) sont une famille de protéines acides exprimées dans les granules des cellules neuroendocrines et immunitaires. Plusieurs peptides dérivés des Cgs présentent des activités antimicrobiennes. L’objectif de ma thèse est d’évaluer l’interaction hôte-pathogène et ensuite de développer un polymère antimicrobien avec insertion du peptide antimicrobien cateslytin (CTL).Dans une première partie, nous avons évalué l’aptitude de la leukotoxine LukE/D à induire la sécrétion des neutrophiles et rôle des protéases bactériennes à dégrader les peptides dérivés de la CgA. Les neutrophiles activés sécrètent de nombreux composés que nous avons identifiés. De plus, la dégradation des PAMs dérivés de la CgA par les protéases de S.aureus a été déterminée. Sur tous les PAMs testés, CTL est le seul qui tue S.aureus et résister à dégradation. Par ailleurs, CgA et CgB sont dégradés par la protéase Glu-C pour produire de nouveaux fragments sans activité antibactérienne, mais d’activité antifongique.Dans une deuxième partie, nous avons décidé de préparer un revêtement conjugué à CTL. CTL-C est utilisé pour préparer des films avec le dépôt alterné de CHI et HA-CTL-C. Par la suite nous avons synthétisé HAFITC-CTL-C and HAFITC pour analyser leur interaction. HAFITC-CTL-C est rapidement détectable dans le cytoplasme sans provoquer la lyse cellulaire. De plus, les films contenant CTL-C ne sont pas toxiques pour les fibroblastes gingivaux humains.En conclusion, CTL est le seul peptide antimicrobien dérivé de la CgA qui peut tuer S.aureus et résiste à la dégradation protéolytique, ce qui est de bon augure pour de nouvelles études visant à développer des biomatériaux antimcrobiens. / Chromogranins (Cgs) are a family of acidic proteins, expressed in secretory granules of neuro-endocrine and immune cells. Several Cgs derived peptides express antimicrobial activity. Current study was aimed to evaluate host-pathogen interaction and ultimately to develop antimicrobial polymer with insertion of cateslytine (CTL).In first part, stimulatory ability of leukotoxin LukE/D to induce neutrophils secretions and role of bacterial proteases to degrade CgA-derived AMPs was evaluated. Activated neutrophils secrete various components which were identified. Later by using antimicrobial assays, several fractions were found active and later discussed with respect to proteomic analysis. Additionally, degradation of CgA derived AMPs by S. aureus proteases was demonstrated. Out of various AMPs tested, CTL was only that can kill S. aureus and resist protease degradation. Furthermore, CgA and CgB are processed by Glu-C protease to produce new fragments lacking antibacterial activity but presenting antifungal activity.Secondly, we aimed to prepare CTL conjugated biomaterial coating. CTL-C was used to prepare PEM films with alternative deposition of CHI and HA-CTL-C and evaluated for antimicrobial activities. Later on, we synthesized HAFITC-CTL-C and HAFITC to analyze their interaction. HAFITC-CTL-C was readily detectable in cytoplasm without provoking cell lysis. Moreover CTL-C inserted PEM films are non-toxic to human gingival fibroblast cells.In conclusion, CTL is the only CgA-derived AMP that can kill S. aureus and resistant to proteolytic degradation, which is a promising feature for further studies in order to develop antimicrobial biomaterials.