Polyalanine peptide variations may have different mechanisms of action against multidrug-resistant bactrial pathogens

© The Author(s) 2021. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved.Objectives: The number of bacterial pathogens resistant to the currently available antibiotics has dramatically increased, with antimicrobial peptides (AMPs) being among the most promising potential new drugs. In this study, the applicability and mechanisms of action of Pa-MAP 2 and Pa-MAP 1.9, two AMPs synthetically designed based on a natural AMP template, were evaluated. Methods: Pa-MAP 2 and Pa-MAP 1.9 were tested against a clinically isolated multidrug-resistant (MDR) Escherichia coli strain. Biophysical approaches were used to evaluate the preference of both peptides for specific lipid membranes, and bacterial surface changes imaged by atomic force microscopy (AFM). The efficacy of both peptides was assessed both in vitro and in vivo. Results: Experimental results showed that both peptides have antimicrobial activity against the E. coli MDR strain. Zeta potential and surface plasmon resonance assays showed that they interact extensively with negatively charged membranes, changing from a random coil structure, when free in solution, to an a-helical structure after membrane interaction. The antibacterial efficacy was evaluated in vitro, by several techniques, and in vivo, using a wound infection model, showing a concentration-dependent antibacterial effect. Different membrane properties were evaluated to understand the mechanism underlying peptide action, showing that both promote destabilization of the bacterial surface, as imaged by AFM, and change properties such as membrane surface and dipole potential. Conclusions: Despite their similarity, data indicate that the mechanisms of action of the peptides are different, with Pa-MAP 1.9 being more effective than Pa-MAP 2. These results highlight their potential use as antimicrobial agents against MDR bacteria.This work was supported by Fundação para a Ciência e a Tecnologia—Ministério da Ciência, Tecnologia e Ensino Superior (FCT-MCTES, Portugal), by Brazilian funding agencies CNPq, CAPES, FADPDF, FINEP and FUNDECT, and by Marie Skłodowska-Curie, Research and Innovation Staff Exchange (MSCA-RISE, EU) project INPACT (call H2020-MSCA-RISE-2014, grant agreement 644167). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. M.R.F. acknowledges the FCT-MCTES fellowship SFRH/BD/100517/2014.info:eu-repo/semantics/publishedVersio