Cytoplasmic membrane thinning observed by interfacial dyes is likely a common effect of bactericidal antibiotics

Abstract

The lipid membrane is a fundamental part of life. However, the effects of different stresses on membranal integrity and physiology are less understood. Using novel 4-aminophthalimide-based membrane-specific dyes (4AP-Cn: n is carbon chain-length), aided with confocal microscopy, fluorescence spectroscopy, molecular dynamics simulations, and flow cytometry, we have studied stress-mediated changes in E. coli membranes. By exploiting the depth-dependent positioning and subsequent environmental sensitivity of the dyes, we have proposed a measure of antibiotic-induced membrane damage: the fluorescence Peak Maxima Difference (PMD) between 4AP-C9 and 4AP-C13. The ROS-influenced PMD quantifies cytoplasmic membrane thickness and measures sensitivity against most bactericidal antibiotics, depending upon the extent of lipid peroxidation. Importantly, we have verified this observation using antibiotic-sensitive and resistant clinical isolates of E. coli and ESKAPE pathogens like K. pneumoniae and Enterobacter spp. This study underscores the role of antibiotic-induced membrane changes; a critical issue given the increasing global antimicrobial resistance.