Interaction of gentamicin sulfate with alginate and consequences on the physico-chemical properties of alginate-containing biofilms

BACKGROUND: Alginate is one of the main extracellular polymeric substances (EPS) in biofilms of Cystic Fibrosis (CF) patients suffering from pulmonary infections. Gentamicin sulfate (GS) can strongly bind to alginate resulting in loss of pharmacological activity; however neither the mechanism nor its repercussion is fully understood. In this study, we investigated how GS modifies the alginate macromolecular network and its microenvironment. MATERIAL AND METHODS: Alginate gels of two different compositions (either enriched in guluronate units (G) or enriched in mannuronate units (M)) were crosslinked with Ca and exposed to GS at varying times and concentrations. The complexes formed were characterized via turbidimetry, mechanical tests, swelling assay, calorimetry techniques, nuclear magnetic resonance, Ca displacement, macromolecular probe diffusion and pH alteration. RESULTS: In presence of GS, the alginate network and its environment undergo a tremendous reorganization in terms of gel density, stiffness, diffusion property, presence and state of the water molecules. We noted that the intensity of those alterations is directly dependent on the polysaccharide motif composition (ratio M/G). CONCLUSION: Our results underline the importance of alginate as biofilm component, its pernicious role during antibiotherapy and could represent a potential macromolecular target to improve anti-infectious therapies

Antibiotic loaded poly(ε-caprolactone) microspheres functionalized with poly(aspartic acid) as bone targeting delivery system to treat infection

INTRODUCTION: The recurrence rate of chronic osteomyelitis in adults is close to 30% [1]. Bacteria are known to migrate deeper into bone tissue through canaliculi and evade common systemic- and local-antibiotic therapies [2]. By fabricating antibiotic loaded poly(ϵ-caprolactone) (PCL) microspheres conjugated with the bone-chelator poly(aspartic acid) (PAA) we aim to prolong the microsphere residency near the site of infection, increasing bactericidal potential. METHODS: Hydrophobic Gentamicin-dioctyl sulfosuccinate (Gen-AOT) loaded PCL microspheres were made by oil/water emulsion methods. In vitro antimicrobial properties were tested by zone of inhibition (ZOI) in a serial plate transfer test with S. aureus. In vivo antimicrobial efficacy of 1 mg of microspheres was tested in a femoral defect in rats (n =5), infected with 2·106 colony forming units (CFU) of bioluminescent Xen-29 a week prior to treatment. In a 2nd study, the PCL microspheres underwent conjugation with PAA by carbodiimide chemistry. Interaction with bone mineral was assessed in the same model as above. IR780 iodide loaded PCL or PCL-PAA microspheres (1 mg) were injected in the bone defect and traced using an in vivo imaging system (IVIS Lumina III, Perkin Elmer). RESULTS & DISCUSSION: ZOI of Gen-AOT loaded PCL was measurable for 5 days, while a ZOI for bactericidal collagen-sheets was visible for 3 days. The Gen-AOT loaded PCL microspheres caused an 81% reduction in CFU compared to untreated control. In vivo, a brighter signal was measured for PCL-PAA compared to PCL microspheres, validating the hypothesis that PAA-grafted PCL resides longer in bone as control PCL. CONCLUSIONS: In the presented animal model, a monotreatment of 1 mg PCL microspheres caused an 81% CFU reduction. PCL-PAA microspheres enhance bone affinity by chelation of the PAA to bone mineral at the femoral defect. Further work is required to optimize the bone-targeted drug delivery system to bone