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UBC Theses and Dissertations

Production, characterization, and biodistribution of lignin-capped silver nanoparticles to combat multidrug resistant bacteria in vitro and in vivo Asnis, Jason


One of the most important issues in healthcare today is the development of bacterial resistance to antibiotics which has created a generation of bacteria known as multidrug resistant (MDR) bacteria. Due to antibiotics’ inability to treat these MDR bacteria metal and metal oxide nanoparticles have been gaining interest as antimicrobial agents. Among those, silver nanoparticles have been used extensively as broad spectrum antimicrobial agents. Here we describe the production and characterization of silver nanoparticles made from the wood biopolymer lignin as a reducing and capping agent with excellent antimicrobial activity against MDR bacteria both in vitro and in vivo. We describe and compare the productions of these lignin-capped silver nanoparticles (L-AgNPs) both through a standard heating procedure and through a microwave-assisted synthesis. The L-AgNPs have been radioactively labeled using both iodine-123 and the novel radioisotope silver-111 to determine their biodistribution by SPECT/CT imaging after subcutaneous injection or intratracheal instillation. The particles were then tested for in vitro antimicrobial activity by broth dilution against a variety of Gram-positive and Gram-negative MDR clinical isolate bacterial strains and ATCC strains. They were also tested for efficacy in an in vivo cutaneous infection (abscess) model caused by biofilm-forming MDR bacterial strains. The particles were produced using a simple, one-pot synthesis method and characterized by ultraviolet-visual spectroscopy, dynamic light scattering, x-ray diffraction, and scanning transmission electron microscopy. Characterization of the lignin-capped silver nanoparticles shows uniform spherical nanoparticles with a silver core and a lignin coating with a diameter of about 50 nm for both synthesis methods, but the microwave method was significantly faster (10 min vs. 3 days). The particles radioactively labeled with silver-111 were visible on SPECT/CT and were labeled with high efficiency, but produced a poor size distribution. The L-AgNPs radioactively labeled with iodine-123 and injected subcutaneously remained at the injection site up to 48 hours post-injection. The in vitro minimum inhibitory concentration (MIC) of L-AgNPs was ≤5 µg/mL for all tested bacterial strains, and a significant decrease in both abscess size and bacterial load was observed against in vivo infections caused by MDR strains of S. aureus and P. aeruginosa.

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