aureus. Interestingly, no planktonic growth inhibition was observed at concentrations able to reduce biofilm formation, and also AMPs with poor killing capacity against some planktonic cells showed anti-biofilm effects. These observations

suggest that BMAP-27, BMAP-28 and P19(9/B) may interfere with biofilm formation by different mechanisms other than direct antimicrobial activity similarly to what observed with the human cathelicidin LL-37 [33], and recently reviewed by Batoni et al. [34]. Most CF patients are infected by P. aeruginosa whose persistence is due to the formation of antibiotic resistant biofilms in the lung [35]. Our results showed that BMAP-27, BMAP-28, and P19(9/B) were also as effective as Tobramycin in reducing cell viability of preformed biofilms MK-0457 formed by GSK1120212 nmr selected strains BVD-523 solubility dmso of P. aeruginosa. At MIC concentrations, and even more at 5xMIC values, the two cathelicidins caused highly significant reduction of biofilm

viability of all six strains of P. aeruginosa whereas Tobramycin showed comparable results only for five isolates. It has previously been reported that extracellular DNA is an important biofilm component [36], and that in P. aeruginosa it is involved in cell-cell attachment and biofilm development [37]. Due to the high affinity of cationic AMPs for DNA [38], it may be presumed that this binding might facilitate the detachment or disruption of otherwise-stable biofilm structures. Conclusions The overall results of this study shed new insights on the antibacterial properties of α-helical peptides, allowing the selection of those with the best properties to cope with lung pathogens associated to CF. BMAP-27, BMAP-28 and also the rationally designed P19(9/B) may thus be considered useful not only as lead compounds for the development of novel antibiotics but also for compounds that may counteract bacterial biofilm formation and eradicate preformed biofilms, reflecting the modern understanding of the role of biofilm formation in chronic CF infections.

However, before applying these molecules in the future Florfenicol for early prophylactic and therapeutic treatment of CF lung disease, further in vitro studies (against other CF pathogens, such as Burkholderia cepacia, and fungi), as well as in vivo studies are needed to evaluate their therapeutic potential. Methods Bacterial strains Overall, 67 antibiotic-resistant bacterial strains were tested in the present study: 15 S. aureus, 25 P. aeruginosa, and 27 S. maltophilia. Strains were collected from respiratory specimens obtained from patients admitted to the CF Operative Unit, “Bambino Gesù” Children’s Hospital and Research Institute of Rome. Identification to species level was carried out by both manual (API System; bioMérieux, Marcy-L’Etoile, France) and automated (BD Phoenix; Becton, Dickinson and Company, Buccinasco, Milan, Italy) biochemical test-based systems.