David Cool (Committee Member), Dan Halm (Committee Member), Saber Hussain (Advisor), Mill Miller (Committee Member), Courtney Sulentic (Advisor)
Doctor of Philosophy (PhD)
Silver nanoparticles (AgNPs) are the fastest growing sector of nanotechnology, due mostly to their antibacterial properties. The antibacterial effectiveness of AgNPs is well known and derives from the shedding of silver ions which have multiple antibacterial targets in the bacterial cell. Due to their continuous release of ions and demonstrated antibacterial potency, some predict that AgNPs have a low potential for resistance development, which would make them a valuable asset in wound management. The ability for AgNPs to cause oxidative imbalance in mammalian cells is also well known, but the potential long-term impact of such a stress has not been studied despite its implication for negative outcomes in wound management. In this thesis, I demonstrate by using a stepwise increasing exposure protocol that Pseudomonas aeruginosa, but not Acinetobacter baumannii or Staphylococcus aureus could develop resistance to 10 nm, citrate-coated AgNPs. The potential for resistance development was lower than the antibacterial drug, ciprofloxacin, but not as low as silver nitrate to which none of the bacteria developed resistance. The resistance mechanism is not yet clear but appeared to involve the phenazine pigments produced by P. aeruginosa which can bind and reduce silver ions. In mammalian cells, I demonstrated the persistence and time-dependent oxidative stress of AgNPs in the A549, epithelial cell model, by using specialized imaging techniques and a common probe for oxidative stress. In addition, I showed that AgNPs can induce a senescent-like phenotype in A549 cells after an exposure that appears non-toxic in the typical viability assays used for assessing cytotoxicity. I confirmed that senescence was induced by showing an increase in senescence-associated, beta-galactosidase activity and the hypertrophic morphology of exposed cells, as well as a decrease in proliferation. The implication of this research for wound management is that AgNPs can be properly applied to wounds in order to inhibit bacterial colonization with little potential for resistant strains to emerge; however, the nanoparticles may persist in wound-associated, mammalian cells. There, the AgNPs will cause persistent oxidative stress with the potential to induce cellular senescence and reduce the long-term health and function of the surrounding tissue.
Department or Program
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