Nanospray treatment of biofilm infections in wounds

PROJECT SUMMARY/ABSTRACT Microbial biofilm infections are a leading complication in healing of wounds arising in a multitude of settings, including severe burns, non-healing pressure ulcers, dog bites, surgical site infections, and gunshot wounds. Infection impairs the wound healing process and is associated with substantial morbidity and mortality. A recent meta-analysis indicates that the prevalence of biofilms in chronic non-healing wounds is 78% [1]. Biofilm formation imparts resistance to antibiotics through innate resistance factors including the drug diffusion barrier of the biofilm's extracellular polymeric substances (EPS) and through induced changes in gene expression, cell signaling and metabolism. Significant correlations have been demonstrated between biofilm formation and multi-drug resistance (MDR) in diverse clinical isolates from wounds [2]. An additional complication is that biofilm formation and progression are not visible to the naked eye; as a result, biofilm infections are not discerned until they are well established and recalcitrant to treatment. A key barrier to identification and treatment of biofilm infections is penetration of their EPS in order for an imaging contrast agent or therapeutic to reach the infecting bacteria. Penetration of biofilms by surfactants, primarily through detergency and surface energy modifications that inhibit bacterial adhesion, may offer a solution to this problem. Strong surfactants such as Tween 20 and Triton X-100 have been shown to disperse biofilms but are too cytotoxic for systemic clinical applications. Polymeric surfactants such as poly(acrylic acid) polyelectrolyte, Carbopol 934TM, and poly(alkylene oxide), Poloxamer 407TM, inhibit biofilm formation but are non-specific and are not strongly antimicrobial [3]. We have recently developed novel graft polyelectrolyte surfactants (PS) that combine the functionalities of these previously used materials with the ability to encapsulate into nanoparticles and deliver cationic antimicrobials (CAMs), with the result being enhanced activity against biofilms in vitro. We propose that such PS can be employed in the wound infection environment, both for imaging and for treatment, by formulation into a “nanospray” that is able to achieve broad coverage within the wound bed, avoid rapid clearance of dyes or of active CAMs in the highly active regenerating wound environment, and penetrate biofilm barriers via the polyelectrolyte surfactant detergency. In order to test this hypothesis, we will: (1) expand the repertoire of CAMs that can achieve favorable nanoformulation with the PS; (2) evaluate the ability of nanospray PS-CAM formulations to treat biofilms in vitro and in vivo; and (3) develop and evaluate the ability of PS-CAM-ICG (where ICG = indocyanine green) formulations to image biofilm formation.