title: Antibacterial effect of chronic exposure of low concentration ZnO nanoparticles on E. coli.
abstract: The toxicity effect due to chronic exposure of ZnO nanoparticles (NPs) was systematically studied by repeatedly treating different lower concentrations of ZnO nanoparticles with culture media of E. coli strain. The chronic exposure of ZnO NPs of concentrations below minimum inhibitory concentration (MIC) exhibited higher toxicity than the single exposure of higher concentrations. Most striking result was 57% inhibition of growth corresponding to chronic exposure of 0.06 mg/mL of ZnO NPs which was two folds more than that exhibited by single exposure of 0.30 mg/mL ZnO NPs. The toxicity of ZnO NPs in E. coli was studied in the light of formation of reactive oxygen species (ROS), measured as malondialdehyde (MDA) equivalent by thiobarbituric acid-ROS (TBARS) assay, and effect of Zn dissolution from ZnO NPs. Higher inhibition of growth for the chronic exposure batches were correlated with higher ROS generation, which subsequently contributed to cause membrane lipid peroxidation, confirmed from observation of cell wall deformation by scanning electron microscopy study and energy dispersive X-ray analysis showed adherence of ZnO NPs on cell wall. The possibility of membrane lipid peroxidation was addressed by revealing in vitro oxidation of oleic acid, which is a monounsaturated fatty acid. Further in this study we have shown that the dissolution of ZnO NPs at pH 7.4 was not significant to cause Zn-induced toxicity.
authors.affiliation: Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee, India. duttafcy@iitr.ernet.in
authors.forename: R K
authors.initials: RK
authors.lastname: Dutta
authors.forename: Bhavani P
authors.initials: BP
authors.lastname: Nenavathu
authors.forename: Mahesh K
authors.initials: MK
authors.lastname: Gangishetty
authors.forename: A V R
authors.initials: AV
authors.lastname: Reddy
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology* / Q000633:toxicity*; D004305:Dose-Response Relationship, Drug; D004926:Escherichia coli / Q000187:drug effects* / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D015227:Lipid Peroxidation; D008315:Malondialdehyde / Q000378:metabolism; D053768:Metal Nanoparticles / Q000633:toxicity*; D008826:Microbial Sensitivity Tests; D008855:Microscopy, Electron, Scanning; D019301:Oleic Acid; D017382:Reactive Oxygen Species / Q000378:metabolism; D017392:Thiobarbituric Acid Reactive Substances / Q000378:metabolism; D036401:Toxicity Tests, Chronic; D015034:Zinc Oxide / Q000494:pharmacology* / Q000633:toxicity*
chemical_list: D000900:Anti-Bacterial Agents; D017382:Reactive Oxygen Species; D017392:Thiobarbituric Acid Reactive Substances; D019301:Oleic Acid; D008315:Malondialdehyde; D015034:Zinc Oxide