Membranolytic Effects of KT2 on Gram-Negative Escherichia coli Evaluated by Atomic Force Microscopy

KT2 is a cationic antimicrobial peptide belonging to Crocodylus siamensis leucrocin I analogs. The mode of action of this compound taken at lethal concentration includes translocation into bacterial cells where binding to DNA is presumed to occur. However, the effects of KT2 on bacterial membrane have not been completely elucidated to date. In this study, a LIVE/DEAD staining technique was used to estimate the appropriate time of peptide-bacteria interaction. The results indicated more than 90% of Escherichia coli population was killed at density of ∼5 × 10⁸ CFU/mL within 30 min after treatment with KT2 at MIC and 10 × MIC. The effects of KT2 on bacterial cells were investigated by the atomic force microscopy (AFM). At near MICs, the peptide induced heavy indentation of the bacterial surface as well as cellular collapse. Conversely, at concentrations of several times the MIC the potential to kill bacteria was greatly increased as judged by the induction of multiple membrane buds on the cell surface. Therefore, the collected results indicate that KT2 can cause different effects on bacterial surface which are positively correlated in magnitude and severity with peptide concentration via membranolytic effects.