Oxidative destabilization of model E. coli membrane by Cu(OH)2 nanoparticles: a neutron reflectometry study

Abstract

The rapid rise in antibiotic resistance of several bacterial strains poses a major threat to the efficacy of existing antibiotics. The development of new antimicrobial compounds to treat bacterial infections has indeed become one of the most urgent commitments of this century, both for therapeutics and for purification and decontamination purposes. The use of compounds producing reactive oxygen species (ROS), such as hydroxyl radicals, has been proposed recently as an effective alternative to classical antibacterial agents. Among the suitable compounds, we have focused on the effect of copper hydroxide nanoparticles, Cu(OH)₂ (which produce OH˙ radicals in presence of hydrogen peroxide, H₂O₂) on the structure and stability of a biomimetic membrane of Escherichia coli. Our results showed that millimolar concentrations of H₂O₂ were sufficient to prompt the production of ROS from Cu²⁺ and Cu⁺/Cu³⁺ ions by a Fenton-like redox cycling, which reacted with the lipid unsaturation and broke the symmetric bilayer ordering. By neutron reflectometry we characterized the lipid bilayer structure before and after the exposure to the nanoparticles, and we found that more than 50% of the original bilayer was converted into a single lipid layer, a consequence of its lysis upon peroxidation. This study builds the pillar of a simple but very accurate method to investigate lipid bilayer degradation by bacterial nanoparticles, with the possibility of screening over various membrane composition, nanoparticles chemistry and oxidative media.