Linear and cyclic short cationic peptides as antibiotic potentiators against drug resistant Gram-negative bacteria

• Main Author: Tan, Ee Heng
• Other Authors: Surajit Bhattacharyya
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Science::Biological sciences
• Online Access: https://hdl.handle.net/10356/148439
• Institution: Nanyang Technological University

Treatment of gram-negative bacteria infections presents a challenge predominantly due to asymmetrical distribution of Lipopolysaccharide(LPS) in the outer leaflet of outer membrane, posing a permeability barrier to various anti-microbial agents. Consequently, anti-microbial peptides that perturb the outer membrane have been explored as adjuvants to complement antibiotic therapy. In the present study, two cationic peptides, linear YL14 and cyclic YI12, were evaluated for their antibiotic potentiation abilities through synergy checkerboard assay. Both peptides appeared to potentiate hydrophobic antibiotics like erythromycin and novobiocin to a greater extent than the large hydrophilic vancomycin. This effect, however, seems to be limited against the biofilm and capsule forming drug resistant Acinetobacter baumanii, with greater effect in non-capsular Pseudomonas aeruginosa, and non-biofilm forming but capsular Klebsiella pneumoniae. Mode of action by YL14 was subsequently investigated, wherein its insertion into hydrophobic milieu of LPS micelle with Kd of 6.78μM was demonstrated through intrinsic tryptophan fluorescence assay while disruption of outer membrane integrity was reflected by dose dependent increased uptake of the fluorescence probe, 1-N-phenylnaphthylamine, by Escherichia coli. NMR revealed a more defined helical conformation of LPS bound YL14 compared to free form, where in silico modelling predicted two potential independent binding modes with LPS.