title: Dissolution of silver nanowires and nanospheres dictates their toxicity to Escherichia coli.
abstract: Silver nanoparticles are extensively used in antibacterial applications. However, the mechanisms of their antibacterial action are not yet fully explored. We studied the solubility-driven toxicity of 100 × 6100 nm (mean primary diameter × length) silver nanowires (NWs) to recombinant bioluminescent Escherichia coli as a target representative of enteric pathogens. The bacteria were exposed to silver nanostructures in water to exclude the speciation-driven alterations. Spherical silver nanoparticles (83 nm mean primary size) were used as a control for the effect of NPs shape. Toxicity of both Ag NWs and spheres to E. coli was observed at similar nominal concentrations: the 4h EC50 values, calculated on the basis of inhibition of bacterial bioluminescence, were 0.42 ± 0.06 and 0.68 ± 0.01 mg Ag/L, respectively. Dissolution and bioavailability of Ag from NWs and nanospheres, analyzed with AAS or Ag-sensor bacteria, respectively, suggested that the toxic effects were caused by solubilized Ag(+) ions. Moreover, the antibacterial activities of Ag NWs suspension and its ultracentrifuged particle-free supernatant were equal. The latter indicated that the toxic effects of ~80-100 nm Ag nanostructures to Escherichia coli were solely dependent on their dissolution and no shape-induced/related effects were observed. Yet, additional nanospecific effects could come into play in case of smaller nanosilver particles.
authors.affiliation: Institute of Physics, University of Tartu, Riia 142, 51014 Tartu, Estonia.
authors.forename: Meeri
authors.initials: M
authors.lastname: Visnapuu
authors.forename: Urmas
authors.initials: U
authors.lastname: Joost
authors.forename: Katre
authors.initials: K
authors.lastname: Juganson
authors.forename: Kai
authors.initials: K
authors.lastname: Künnis-Beres
authors.forename: Anne
authors.initials: A
authors.lastname: Kahru
authors.forename: Vambola
authors.initials: V
authors.lastname: Kisand
authors.forename: Angela
authors.initials: A
authors.lastname: Ivask
mesh_terms: D000900:Anti-Bacterial Agents / Q000008:administration & dosage; D004926:Escherichia coli / Q000187:drug effects*; D053768:Metal Nanoparticles / Q000737:chemistry; D054118:Nanospheres / Q000008:administration & dosage* / Q000737:chemistry; D053770:Nanowires / Q000008:administration & dosage* / Q000737:chemistry; D012834:Silver / Q000008:administration & dosage* / Q000737:chemistry
chemical_list: D000900:Anti-Bacterial Agents; D012834:Silver
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