Based on the 2017 report by WHO Global Antimicrobial Surveillance system, antibiotic resistant bacteria (ARB) have become a worldwide challenge with growing need to be tackled. Current approaches to eliminate ARBs include antibiotic cocktails, engineered bacteriophages, monoclonal antibodies and antimicrobial peptides aimed at targeting multiple bacterial pathways. However, the use of antibiotic cocktails is limited by the increased risk of developing resistance, whereas antibodies, bacteriophages and peptides are susceptible to proteolytic degradation compromising their antimicrobial efficacy. A nanoparticle-based alternative has been recently explored as a promising solution to overcome the current challenges to eliminate ARBs. Silver nanoparticles (AgNPs) have gained a lot of attention for this purpose in the last few years. AgNP’s antibacterial property is associated with the leaching of silver ion (Ag⁺), which leads to bacterial cell membrane disruption affording the killing of bacteria. However, the use of AgNPs is limited by slow release of Ag⁺ that impacts their antibacterial activity. In this study, to increase the Ag⁺ release, we conjugated a photosensitizer (protoporphyrin (PpIX)) to the surface of AgNPs. The hypothesis of this project relies on the generation of reactive oxygen species after PpIX has been irradiated with light, which oxidize AgNPs to enhance the production of Ag⁺. In addition, we also expect to observe a synergistic effect due to the known antibacterial properties of photosensitizers. PpIX molecule was chemically attached to AgNPs using conjugation chemistry. The final product (PpIX-AgNPs) was characterized using FT-IR, TGA, DLS and Zeta-potential. The amount of PpIX grafted on the surface of AgNPs was determined using UV-vis spectroscopy. ICP-OES was used to quantify the release of Ag⁺ from PpIX-AgNPs upon light irradiation. The synergistic effect was evaluated in two antibiotic resistant bacterial strains: Methicillin resistant Staphylococcus aureus (MRSA) and Escherichia coli (E. coli) resistant to ampicillin, sulfamethoxazole, ciprofloxacin, and tetracycline. The synergistic effect of PpIX-AgNPs to eliminate ARB was demonstrated using the colony count method and its efficacy was determined based on the minimum inhibitory concentration (MIC).

Juan Vivero

University of North Carolina at Charlotte

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