Multidrug-resistant (MDR) bacterial infections represent a serious life-threat causing almost 50,000 deaths per year in Europe and in the US; and this number is expected to grow up to tenfold by 2050, killing more than cancer1, 2. In particular, pulmonary infections due to the Gram-negative bacterium Pseudomonas aeruginosa remain one of the major cause of morbidity and mortality3, either in intensive care units or in ventilated patients, as well as in cystic fibrosis (CF) sufferers, complicating therapy in the CF airways4–7. In parallel, the decrease in the pharmaceutical industry research pipeline for novel antimicrobial agents during the last three decades has resulted in an urgent need for the discovery of new strategies to address the vital problems of infectious diseases8, 9. Naturally occurring antimicrobial peptides (AMPs) or their derivatives stand for an appealing source for the generation of new therapeutics9–16. AMPs are ubiquitous in nature and act as the first line of defence against invading microorganisms17, 18. Although human lung epithelial cells produce AMPs (e.g. defensins and the cathelicidins LL-37)19, 20, most of them are present at very low concentrations and are salt-sensitive in vitro making it difficult for them to be active in the abnormally low pH and high-salt environment existing at the apical side of CF epithelial cells21–23. A promising therapeutic approach to defeat P. aeruginosa lung infections would be to exogenously apply AMPs in the lung environment. We recently identified a short-sized (21 amino acids long) derivative of the frog-skin AMP esculentin-1a, named Esculentin-1a(1–21)NH2 [GIFSKLAGKKIKNLLISGLKG-NH2, Esc(1–21)]24, 25, with the following attractive features: (i) a potent and rapid killing kinetics against both planktonic and biofilms forms of P. aeruginosa strains, with a pronounced membrane-perturbing activity as a plausible mode of action26. This is a highly non-specific mechanism which limits the induction of resistance compared to the highly selective conventional antibiotics e.g. tobramycin and ciprofloxacin that would no longer be able to recognize their specific and single target, after mutation27; (ii) the ability to preserve antimicrobial activity at high ionic strength, in contrast with the majority of AMPs of mammalian origin28; (iii) the ability to detoxify, in vitro, P. aeruginosa lipopolysaccharide (LPS), by inhibiting the release of TNF-α from LPS-activated macrophages28.