Antimicrobial activity of natural and synthetic peptides against P. aeruginosa and other clinically relevant bacterial pathogens

Antimicrobial resistance represents one of the most urgent challenges in modern medicine, threatening the effectiveness of conventional antibiotic therapies and complicating the management of infectious diseases. Within this context, Pseudomonas aeruginosa – a wellrecognized member of the ESKAPE group – stands out due to its high virulence, metabolic adaptability, and intrinsic resistance mechanisms, which allow it to persist in diverse environments and evade standard treatments. These characteristics make it an important target for the development of innovative antimicrobial strategies aimed at overcoming its adaptive defences. A novel strategy to address this pressing challenge involves the use of antimicrobial peptides (AMPs), which have already demonstrated broad-spectrum activity and show potential as therapeutic agents against infections caused by multidrug-resistant bacteria. Within this framework, the synthetic peptide SET-M33L and its PEGylated analogue SET-M33LPEG emerge as particularly promising candidates, as multiple studies have consistently confirmed their efficacy in eradicating bacterial pathogens across several infection models. In this project, their antimicrobial efficacy was further evaluated on both reference strains and clinical isolates through assessments of minimum inhibitory concentrations (MIC), minimum biofilm eradication concentrations (MBEC), and cell viability in biofilm after the peptide administration. Complementary transcriptomic analyses of peptide-treated cultures revealed a significant down-regulation of genes associated with virulence, including those involved in secretion systems and exotoxin production, alongside an up-regulation of nitrogen metabolism pathways. Furthermore, MALDI-TOF analyses of biofilms highlighted substantial changes in protein composition following peptide treatment, indicating that the peptide leads to measurable modifications in biofilm structure and molecular content. In addition, naturally occurring peptides were also investigated. Temporin A and Aib8-Esc(1–21), as well as Bac7-derived peptides, B7-005 and B7-007, were selected based on their reported efficacy and evaluated for stability using analytical techniques such as HPLC and MALDI-TOF. The most stable peptides were subsequently prioritized for in vivo efficacy studies in a lung infection model, currently under development. Collectively, these investigations provide insights into the antimicrobial potential and mechanistic effects of both synthetic and natural antimicrobial peptides, highlighting their promise as novel therapeutic alternatives to conventional antibiotics in the fight against multidrug-resistant pathogens.