title: Silver nanoparticles embedded in zeolite membranes: release of silver ions and mechanism of antibacterial action.
abstract: BACKGROUND
  The focus of this study is on the antibacterial properties of silver nanoparticles embedded within a zeolite membrane (AgNP-ZM).
  
  
  RESULTS
  These membranes were effective in killing Escherichia coli and were bacteriostatic against methicillin-resistant Staphylococcus aureus. E. coli suspended in Luria Bertani (LB) broth and isolated from physical contact with the membrane were also killed. Elemental analysis indicated slow release of Ag(+) from the AgNP-ZM into the LB broth. The E. coli killing efficiency of AgNP-ZM was found to decrease with repeated use, and this was correlated with decreased release of silver ions with each use of the support. Gene expression microarrays revealed upregulation of several antioxidant genes as well as genes coding for metal transport, metal reduction, and ATPase pumps in response to silver ions released from AgNP-ZM. Gene expression of iron transporters was reduced, and increased expression of ferrochelatase was observed. In addition, upregulation of multiple antibiotic resistance genes was demonstrated. The expression levels of multicopper oxidase, glutaredoxin, and thioredoxin decreased with each support use, reflecting the lower amounts of Ag(+) released from the membrane. The antibacterial mechanism of AgNP-ZM is proposed to be related to the exhaustion of antioxidant capacity.
  
  
  CONCLUSIONS
  These results indicate that AgNP-ZM provide a novel matrix for gradual release of Ag(+).
authors.affiliation: Department of Pathology, The Ohio State University, Columbus, OH, USA.
authors.forename: Amber
authors.initials: A
authors.lastname: Nagy
authors.forename: Alistair
authors.initials: A
authors.lastname: Harrison
authors.forename: Supriya
authors.initials: S
authors.lastname: Sabbani
authors.forename: Robert S
authors.initials: RS
authors.lastname: Munson
authors.forename: Prabir K
authors.initials: PK
authors.lastname: Dutta
authors.forename: W James
authors.initials: WJ
authors.lastname: Waldman
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects; D008422:Materials Testing; D053768:Metal Nanoparticles / Q000648:ultrastructure; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects; D008855:Microscopy, Electron, Scanning; D050997:Nanomedicine; D020411:Oligonucleotide Array Sequence Analysis; D018384:Oxidative Stress / Q000187:drug effects; D033362:Powder Diffraction; D018894:Reverse Transcriptase Inhibitors; D012834:Silver / Q000494:pharmacology*; D017641:Zeolites
chemical_list: D000900:Anti-Bacterial Agents; D018894:Reverse Transcriptase Inhibitors; D017641:Zeolites; D012834:Silver