Stability of Cytoplasmic Membrane of Escherichia coli Bacteria in Aqueous and Ethanolic Environment

The mechanism of action of any antibacterial agent or disinfectant depends largely on their interaction with the bacterial membrane. Herein, we use the SPICA (surface property fitting coarse graining) force-field and develop a coarse-grained (CG) model for the structure of the cytoplasmic membrane of Escherichia coli (E. coli) and its interaction with water and ethanol. We elucidate the impact of different concentrations of ethanol on the cytoplasmic membrane bilayers and vesicles of E. coli using the CG molecular dynamics (CG MD) simulations. Our modeling approach first focuses on the parametrization of the required force-field for POPG lipid and its interaction with water, ethanol, and POPE lipid. Subsequently, the structural stability of the E. coli bacterial membrane in the presence of high and low concentrations of ethanol is delineated. Both flat bilayers as well as vesicles of E. coli membrane were considered for the CG MD. Our results reveal that, at low ethanol concentrations (<30 mol %), the size of the E. coli vesicles increases with discernible deformations in their shapes. Because of ethanol-induced interdigitation, thinning of the E. coli vesicular membrane is also observed. However, at higher ethanol concentrations (>30 mol %), the integrity of the vesicles is lost because of deteriorating invasion of ethanol molecules into the vesicle bilayer and significant weakening of lipid–lipid interactions. At higher ethanol concentrations (40 and 70 mol %), both the multivesicle and single-vesicle bacterial membranes exhibit a similar rupturing pattern wherein the extraction of lipids from the membrane and formation of aggregates of the component lipids are observed. These aggregates consist of polar head groups of 3–5 POPE/POPG lipids with intertwined nonpolar tails.