Here we used a new strategy for exploring the peptide chemical space to discover bicyclic antimicrobial peptides.

We used the concept of chemical space to explore a virtual library of bicyclic peptides formed by double thioether cyclization of a precursor linear peptide, and identified an antimicrobial bicyclic peptide (AMBP) with remarkable activity against several MDR strains of Acinetobacter baumannii and Pseudomonas aeruginosa.

The peptide α-helix is right-handed when containing amino acids with L-chirality, and left-handed with D-chirality, however mixed chirality peptides generally do not form α-helices unless the non-natural residue amino-isobutyric acid...

A new family of cyclic antimicrobial peptides is reported targeting multidrug resistant Pseudomonas aeruginosa by membrane disruption.

AimIn the present work, the potential of the D-enantiomeric dendrimers dG3KL and dTNS18 was evaluated in relation to tobramycin (Tob), for the development of novel antibacterials to treat Pseudomonas aeruginosa chronic lung infections in patients with cystic fibrosis.ResultsThe activity of dendrimers against planktonic P. aeruginosa cells was less than Tob against three of the four strains tested (median minimum inhibitory concentration [MIC] 8 vs 1 µg/mL, respectively), but 32-fold higher against the PaPh32 strain isolated at posttransplantation stage. Results from comparative minimum bactericidal concentration/MIC evaluation and time–kill assay suggested a bactericidal mechanism for all test agents. Subinhibitory concentrations of both dendrimers and Tob significantly affected biofilm formation by all strains in a dose-dependent manner, although the PaPh26 strain, isolated during the chronic stage of infection, was particularly susceptible to dendrimers. The activity of dendrimers against preformed P. aeruginosa biofilm was generally comparable to Tob, considering both dispersion and viability of biofilm. Particularly, exposure to the test agent at 10 × MIC caused significant biofilm death (>90%, even to eradication), though with strain-specific differences. Single administration of dendrimers or Tob at 10 × MIC was not toxic in Galleria mellonella wax-moth larvae over 96 hours. However, contrarily to Tob, dendrimers were not protective against systemic infection caused by P. aeruginosa in G. mellonella. Kinetics of P. aeruginosa growth in hemolymph showed that bacterial load increased over time in the presence of dendrimers.ConclusionOverall, our findings indicated that dG3KL and dTNS18 peptide dendrimers show in vitro activity comparable to Tob against both P. aeruginosa planktonic and biofilm cells at concentrations not toxic in vivo. Further studies are warranted to explore different dosages and to increase the bioavailability of the peptides to solve the lack of protective effect observed in G. mellonella larvae.