Leucine-Based Polymer Architecture-Induced Antimicrobial Properties and Bacterial Cell Morphology Switching

To evaluate the comparative antibacterial activity of leucine-based cationic polymers having linear, hyperbranched, and star architectures containing both hydrophilic and hydrophobic segments against Gram-negative bacterium, Escherichia coli (E. coli), herein we performed zone of inhibition study, minimum inhibitory concentration (MIC) calculation, and bacterial growth experiment. The highest antibacterial activity in terms of the MIC value was found in hyperbranched and star architectures because of the greater extent of cationic and hydrophobic functionality, enhancing cell wall penetration ability compared to that of the linear polymer. The absence of the bacterial regrowth stage in the growth curve exhibited the highest bactericidal capacity of star polymers, when untreated cells (control) already reached to the stationary phase, whereas the bacterial regrowth stage with a delayed lag phase was critically observed for linear and hyperbranched architectures displaying lower bactericidal efficacy. Coagulation of E. coli cells, switching of cell morphology from rod to sphere, and lengthening due to stacking in an antimicrobial polymer-treated environment at the bacterial regrowth stage in liquid media were visualized critically by field emission scanning electron microscopy and confocal fluorescence microscopy instruments in the presence of 4',6-diamidino-2-phenylindole stain.