Design, Synthesis, and Nanostructure-Dependent Antibacterial Activity of Cationic Peptide Amphiphiles.

The development of bacterial resistant strains is a global health concern. Designing antibiotics that limit the rise of pathogenic resistance is essential to efficiently treat pathogenic infections. Self-assembling amphiphilic molecules are an intriguing platform for the treatment of pathogens because of their ability to disrupt bacterial membranes and function as drug nanocarriers. We have designed cationic peptide amphiphiles (PAs) that can form micelles, nanofibers, and twisted ribbons with the aim of understanding antimicrobial activity at the supramolecular level. We have found that micelle-forming PAs possess excellent antimicrobial activity against various Gram-positive and Gram-negative pathogens, such as methicillin-resistant Staphylococcus aureus (MRSA) and multidrug-resistant Klebsiella pneumoniae with minimal inhibitory concentrations (MICs) ranging between 1 and 8 μg/mL, when compared to nanofibers with MICs >32 μg/mL. The data suggest that the antimicrobial activity of the PAs depends on their morphology, amino acid sequence, the length of the alkyl tail, and the overall hydrophobicity of the PA. Scanning electron microscopy, confocal microscopy, and flow cytometry studies using MRSA and Escherichia coli K12 strains showed that PAs increase cell membrane permeability and disrupt the integrity of pathogen's membrane, leading to cell lysis and death. PAs are a promising platform to develop new antimicrobials that could work as nanocarriers to develop synergistic antibacterial therapies.