Investigations on the membrane interaction of C-terminally amidated esculentin-2 HYba1 and 2 peptides against bacteria.

The membrane interaction and damage caused by C-terminally amidated esculentin-2 peptides identified from the frog skin is illustrated in the present study using Staphylococcus aureus and Vibrio cholerae. Double staining with fluorescent probes SYTOX and DAPI proved the concentration-dependent bacterial membrane damage induced by the peptides. It was found that the sub-MIC of both peptides induced transient pores on the bacterial membrane. These peptides also caused depolarisation on the bacterial membrane during their interaction. The physical changes on bacterial cells like blebbing, elongation, fusion, and so forth upon peptide treatment were visualized through SEM images. The antimicrobial activity of the peptides against S. aureus and V. cholerae was not altered at physiological concentrations of divalent and monovalent cations, which is advantageous in a therapeutic context. The increase of MIC against V. cholerae at higher concentrations of Mg2+ and Ca2+ (>5 µM) is due to the concentration-dependent antagonism exhibited by these ions for the cation binding sites on the bacterial membrane, which facilitates the process of 'self-promoted uptake.' The study emphasizes to utilize the ability of these peptides to produce transient pores at sub-MICs in combinatorial therapy.