1 MODE OF ACTION STUDIES ON SYNTHETIC ANTIMICROBIAL PEPTIDES MASTER THESIS IN MEDICAL BIOLOGY AND MOLECULAR BIOLOGY

Increasing prevalence of bacteria that carries resistance towards conventional antibiotics has prompted the investigation into new compounds for bacterial intervention to ensure efficient infection control in the future. One group of potential lead structures for antibiotics is antimicrobial peptides (AMPs) due to their characteristics as naturally derived compounds with antimicrobial activity. In that perspective, this thesis seeks to characterize the mechanism of action of small library of in silico optimized peptides. Following determination of peptide activity against E.coli, S.aureus and P.aeruginosa, toxicity was assessed revealing meaningful therapeutic indexes for the far majority of the peptides. Investigation of the peptides effect on bacteria uncovered rapid inhibition with signs of bacterial lysis together with increased bacterial size. Both visual and quantitative assays clearly demonstrated bacterial membrane disruption after 10 minutes, although signs of reestablished membrane integrity at lower concentrations were observed after two hours. The membrane disrupting effect was verified by measuring the release of calcein from bacterial mimicking liposomes. This uncovered the most active peptides as inducers of immediate release, indicating the kinetics of membrane permeabilization as an important determinant of bacterial activity. No secondary structure of peptides in the presence of different liposomes was observed, implying that this feature is not essential for bacterial and cytotoxic activity within this library of peptides. In conjunction, these findings provide strong indications of membrane disruption as the primary mechanism of bacterial inhibition for the tested peptides. RESUMÉ En stadig stigende forekomst af bakterier med resistens overfor konventionelle antibiotika ha