Real-Time Observation of Antimicrobial Polycation Effects on Escherichia coli: Adapting the Carpet Model for Membrane Disruption to Quaternary Copolyoxetanes.

Real-time atomic force microscopy (AFM) was used for analyzing effects of the antimicrobial polycation copolyoxetane P[(C12)-(ME2Ox)-50/50], C12–50 on the membrane of a model bacterium, Escherichia coli (ATCC# 35218). AFM imaging showed cell membrane changes with increasing C12–50 concentration and time including nanopore formation and bulges associated with outer bacterial membrane disruption. A macroscale bactericidal concentration study for C12–50 showed a 4 log kill at 15 μg/mL with conditions paralleling imaging (1 h, 1x PBS, physiological pH, 25 °C). The dramatic changes from the control image to 1 h after introducing 15 μg/mL C12–50 are therefore reasonably attributed to cell death. At the highest concentration (60 μg/mL) further cell membrane disruption results in leakage of cytoplasm driven by detergent-like action. The sequence of processes for initial membrane disruption by the synthetic polycation C12–50 follows the carpet model posited for antimicrobial peptides (AMPs). However, the nanoscale...