title: Toxicity mechanisms in Escherichia coli vary for silver nanoparticles and differ from ionic silver.
abstract: Silver nanoparticles (Ag NPs) are commonly added to various consumer products and materials to impair bacterial growth. Recent studies suggested that the primary mechanism of antibacterial action of silver nanoparticles is release of silver ion (Ag(+)) and that particle-specific activity of silver nanoparticles is negligible. Here, we used a genome-wide library of Escherichia coli consisting of ∼4000 single gene deletion mutants to elucidate which physiological pathways are involved in how E. coli responds to different Ag NPs. The nanoparticles studied herein varied in both size and surface charge. AgNO3 was used as a control for soluble silver ions. Within a series of differently sized citrate-coated Ag NPs, smaller size resulted in higher Ag ion dissolution and toxicity. Nanoparticles functionalized with cationic, branched polyethylene imine (BPEI) exhibited equal toxicity with AgNO3. When we used a genome-wide approach to investigate the pathways involved in the response of E. coli to different toxicants, we found that only one of the particles (Ag-cit10) exhibited a pattern of response that was statistically similar to that of silver ion. By contrast, the pathways involved in E. coli response to Ag-BPEI particles were more similar to those observed for another cationic nanoparticle that did not contain Ag. Overall, we found that the pathways involved in bacterial responses to Ag nanoparticles are highly dependent on physicochemical properties of the nanoparticles, particularly the surface characteristics. These results have important implications for the regulation and testing of silver nanoparticles.
authors.affiliation: University of California Center for Environmental Implications of Nanotechnology and ‡California NanoSystems Institute, University of California , Los Angeles, California 90095, United States.
authors.forename: Angela
authors.initials: A
authors.lastname: Ivask
authors.forename: Amro
authors.initials: A
authors.lastname: Elbadawy
authors.forename: Chitrada
authors.initials: C
authors.lastname: Kaweeteerawat
authors.forename: David
authors.initials: D
authors.lastname: Boren
authors.forename: Heidi
authors.initials: H
authors.lastname: Fischer
authors.forename: Zhaoxia
authors.initials: Z
authors.lastname: Ji
authors.forename: Chong Hyun
authors.initials: CH
authors.lastname: Chang
authors.forename: Rong
authors.initials: R
authors.lastname: Liu
authors.forename: Thabet
authors.initials: T
authors.lastname: Tolaymat
authors.forename: Donatello
authors.initials: D
authors.lastname: Telesca
authors.forename: Jeffrey I
authors.initials: JI
authors.lastname: Zink
authors.forename: Yoram
authors.initials: Y
authors.lastname: Cohen
authors.forename: Patricia Ann
authors.initials: PA
authors.lastname: Holden
authors.forename: Hilary A
authors.initials: HA
authors.lastname: Godwin
mesh_terms: D000900:Anti-Bacterial Agents / Q000493:pharmacokinetics / Q000633:toxicity*; D001682:Biological Availability; D004926:Escherichia coli / Q000187:drug effects* / Q000235:genetics / Q000254:growth & development; D053768:Metal Nanoparticles / Q000633:toxicity*; D008826:Microbial Sensitivity Tests; D018625:Microscopy, Atomic Force; D046529:Microscopy, Electron, Transmission; D012834:Silver / Q000737:chemistry / Q000493:pharmacokinetics / Q000633:toxicity*; D012995:Solubility
chemical_list: D000900:Anti-Bacterial Agents; D012834:Silver