In vitro activity of multi-branched peptides against planktonic and biofilm cells of Pseudomonas aeruginosa from cystic fibrosis patients.

Introduction: Treatment of cystic fibrosis (CF)-associated lung infections is hampered by the presence of multidrug resistant pathogens, many of which are also strong biofilm producers such as Pseudomonas aeruginosa. Antimicrobial peptides (AMPs) represent a vast class of antibiotic compounds potentially suitable to address multidrug resistant bacteria. Here we evaluated previously reported antimicrobial peptide dendrimers (AMPDs) and related AMPs in comparison with DJK5 recently reported by the Hancock group, against both planktonic and biofilm lifestyles of P. aeruginosa strains from CF patients. Materials and Methods: Four P. aeruginosa strains collected from CF patients (PaPh13, PaPh14, PaPh29, PaPh32) were selected because strong-biofilm producers. MIC and MBC values were measured by microdilution broth technique according to EUCAST guidelines. The effect of each peptide at sub-inhibitory concentrations (sub-MICs) on biofilm formation was spectrophotometrically evaluated following crystal violet stain. Control (CTRL) biofilms were not exposed to peptides. Results: We identified several potent AMPDs against P. aeruginosa cells showing MIC values ranging from 8 to 16 μg/ml. MBC values were equal or 1-log2 dilution higher than relative MIC values, thus suggesting a bactericidal mechanism of action. All peptides tested affected biofilm formation, although at different extent. Two peptides were most active at sub-MICs against biofilm formation causing a significant, concentration-dependent, reduction of biofilm biomass (compared to CTRL) up to 80 %. DJK5 was the least effective causing reduction of biofilm biomass in 25% of cases. Conclusions: The activity shown by second generation dendrimers peptides against planktonic cells and biofilm formation makes them promising “lead compounds” for future development of novel drugs for therapeutic treatment of CF lung disease. Ongoing work is investigating the activity of AMPs against higher number of strains.