Silver nanoparticles (Ag-Nps) are widely used in industry and medicine, but potential effects of environmental exposures are poorly characterized. This study investigated mechanisms of Ag-Np toxicity in Escherichia coli, with a focus on effects of reactive oxygen species (ROS) production. Because agglomeration causes silver nanoparticles to behave like bulk materials, we confirmed nanostate chemistry by Malvern Zetasizer prior to analyzing antimicrobial effects. These studies demonstrated that silver nanoparticle agglomerations were sensitive to salt concentration and temperature; therefore low salt (0.05% NaCl) Luria Bertoni (LB) broth and low temperature (32° C) conditions were used for subsequent experiments. Silver nanoparticles had a significant effect on E. coli growth kinetics, delaying entry into log-phase growth. Bacterial sensitivity was analyzed via disk-diffusion assays with varying masses of silver nanoparticles per disk (0-25 μg/disk). Significant inhibition of growth was observed at 0.78 μg Ag-Nps/disk. Minimum inhibitory concentration (MIC) and minimum bactericidal concentrations (MBC) tests performed in LB broth supplemented with varying concentrations of silver nanoparticles (1-100 μg/mL) demonstrated the MIC for silver nanoparticles was 120 μg/mL; the MBC was 150 μg/mL. Intracellular ROS levels were measured with 2’7’ – dichlorofluorescin diacetate DCFDA staining: a significant increase of intracellular ROS was detected at 1.562 μg Ag-Nps/mL. Protein carbonyl formation was measured using a colorimetric assay and lipid peroxidation measured by the TBARS assay to assess Ag-Np effects on macromolecules. Silver nanoparticles significantly increased protein carbonyl formation, lipid peroxidation, and structural DNA damage at 3.125 μg/mL. These studies indicate that silver nanoparticles inhibit microbial growth and induce ROS and oxidative stress at sub-MIC concentrations. Such knowledge can contribute to the ecological risk assessment of emerging contaminants even where environmental levels of contamination are below levels of microbial inhibition.
|Commitee:||Lin, Zhi-Qing, McCracken, Vance, Theodorakis, Chris|
|School:||Southern Illinois University at Edwardsville|
|School Location:||United States -- Illinois|
|Source:||MAI 56/03M(E), Masters Abstracts International|
|Subjects:||Biology, Toxicology, Surgery, Microbiology|
|Keywords:||Escherichia coli, Reactive oxygen species, Silver nanoparticles, Toxicology|
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