title: A novel mechanism for the antibacterial effect of silver nanoparticles on Escherichia coli.
abstract: Silver nanoparticles are known to have antimicrobial properties and have been used extensively in medicine, although the mechanism(s) of action have not yet been clearly established. In the present study, the findings suggest a novel mechanism for the antibacterial effect of silver nanoparticles on Escherichia coli, namely, the induction of a bacterial apoptosis-like response. We propose a possible mechanism for the bacterial apoptosis-like response that includes the following: accumulation of reactive oxygen species (ROS) (detected with H2DCFDA staining), increased intracellular calcium levels (detected with Fura-2 AM), phosphatidylserine exposure in the outer membrane (detected with Annexin V) which is the hallmarks of early apoptosis, disruption of the membrane potential [detected with DiBAC4(3)], activation of a bacterial caspase-like protein (detected by FITC-VAD-FMK staining) and DNA degradation (detected with TUNEL assay) which is the hallmarks of late apoptosis in bacterial cells treated with silver nanoparticles. We also performed RecA expression assay with western blotting and observed activation of SOS response to repair the damaged DNA. To summarize, silver nanoparticles are involved in the apoptosis-like response in E. coli and the novel mechanisms which were identified in this study, suggest that silver nanoparticles may be an effective antimicrobial agent with far lower propensity for inducing microbial resistance than antibiotics.
authors.affiliation: School of Life Sciences, BK 21 Plus KNU Creative BioResearch Group, College of Natural Sciences, Kyungpook National University, Daehak-ro 80, Buk-gu, Daegu, 702-701, Republic of Korea.
authors.forename: Wonyoung
authors.initials: W
authors.lastname: Lee
authors.forename: Keuk-Jun
authors.initials: KJ
authors.lastname: Kim
authors.forename: Dong Gun
authors.initials: DG
authors.lastname: Lee
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000032:analysis; D002118:Calcium / Q000032:analysis; D002462:Cell Membrane / Q000187:drug effects; D053938:DNA Fragmentation; D004260:DNA Repair; D004269:DNA, Bacterial / Q000187:drug effects; D004353:Drug Evaluation, Preclinical; D004926:Escherichia coli / Q000187:drug effects*; D008563:Membrane Lipids / Q000032:analysis; D053768:Metal Nanoparticles; D008826:Microbial Sensitivity Tests; D009643:Norfloxacin / Q000494:pharmacology; D010718:Phosphatidylserines / Q000032:analysis; D017382:Reactive Oxygen Species / Q000378:metabolism; D012834:Silver / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D008563:Membrane Lipids; D010718:Phosphatidylserines; D017382:Reactive Oxygen Species; D012834:Silver; D009643:Norfloxacin; D002118:Calcium