Short Antimicrobial Peptides Based on Arginine and Tryptophan: Agents with Potential in Combating Resistant Pathogens

The limitations of conventional antibiotics due to the rise of antimicrobial resistance demand new therapeutic strategies. Antimicrobial peptides represent a promising alternative because of their broad-spectrum activity and low propensity for inducing resistance. In this study, we designed and evaluated a set of seven-residue Arg/Trp-based peptides. All peptides were successfully synthesized and characterized, and their activities were assessed against Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus, including clinical isolates. Among the sequences tested, (WRW)₂F exhibited the strongest antimicrobial activity, displaying bactericidal effects. Growth inhibition and time-kill assays showed dose-dependent effects, and SYTOX Green uptake, AFM, and TEM analyses confirmed rapid membrane permeabilisation and structural disruption as the primary mode of action, while it has been demonstrated not to act as an efflux pump inhibitors. Importantly, the three more active peptides synergized with linezolid against E. coli, and (WRW)₂F was able to resensitize MRSA to oxacillin, demonstrating their potential for combined therapies. The toxicity studies in eukaryotic cells and the C. elegans survival model have shown a favorable safety profile. Overall, this work highlights short Arg/Trp-rich peptides, especially (WRW)₂F, as affordable, easy-to-synthesize, and biocompatible compounds with significant potential to enhance antibiotic efficacy and counteract resistant pathogens.