Antimicrobial activity of silver loaded MnO2 nanomaterials with different crystal phases against Escherichia coli

Abstract

Silver-loaded MnO2 nanomaterials (Ag/MnO2), including Ag/alpha-MnO2, Ag/beta-MnO2, Ag/gamma-MnO2 and Ag/delta-MnO2 nanorods, were prepared with hydrothermal and impregnation methods. The bactericidal activities of four types of Ag/MnO2 nanomaterials against Escherichia coli were investigated and an inactivation mechanism involving Ag+ and reactive oxygen species (ROS) was also proposed. The bactericidal activities of Ag/MnO2 depended on the MnO2 crystal phase. Among these nanomaterials, Ag/beta-MnO2 showed the highest bactericidal activity. There was a 6-log decrease in E. coli survival number after treatment with Ag/beta-MnO2 for 120 min. The results of 5,5-dimethyl-1-pyrroline-N-oxide spin-trapping measurements by electron spin resonance indicate UOH and UO2 -formation with addition of Ag/beta-MnO2, Ag/gamma-MnO2 or Ag/delta-MnO2. The strongest peak of UOH appeared for Ag/beta-MnO2, while noUOH or UO2 signal was found over Ag/alpha-MnO2. Through analysis of electron spin resonance (ESR) and Ag+ elution results, it could be deduced that the toxicity of Ag+ eluted fromAg/MnO2 nanomaterials and ROS played the main roles during the bactericidal process. Silver showed the highest dispersion on the surface of beta-MnO2, which promoted ROS formation and the increase of bactericidal activity. Experimental results also indicated thatAg/MnO2 induced the production of intracellular ROS and disruption of the cell wall and cell membrane. (C) 2015 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V