Antimicrobial Peptide Conjugated Gold Nanoparticles: Synthesis, Characterization and Antimicrobial Activity Studies

Abstract

The escalation of multidrug-resistant pathogens has created a dire need to develop novel ways of addressing this global therapeutic challenge. Because of their antimicrobial activities, combination of antimicrobial peptide (AMP) and nanoparticles (NPs) is a promising tool to kill antibiotic-resistant strains. This thesis describes the design, synthesis and antimicrobial evaluation of lipopeptide conjugated gold nanoparticles (AuNPs). The first part of the thesis describes studies towards the design and synthesis of AMP conjugated gold nanoparticles. Lipopeptide 3163 (Cys-lipopeptide 17) was synthesized by manual solid phase peptide synthesis and purified using RP-HPLC (96.25% purity). Cysteine at N-terminus was added to covalently conjugate to gold nanoparticle via Au-thiol bond. The success of the conjugation was determined by Fourier transform infrared spectroscopy (FTIR), zeta potential and transmission electron microscopy (TEM). The second part of this thesis describes the antimicrobial activity studies of lipopeptide 3163 and lipopeptide 3163 conjugated gold nanoparticles. The minimum inhibitory concentration (MIC) of lipopeptide 3163 conjugated gold nanoparticles against Gram-negative Escherichia coli. (E. coli) and Pseudomonas aeruginosa. (P. aeruginosa) strains, showed enhanced antibacterial activity than lipopeptide 3163 alone, with four-fold and two-fold increase observed, respectively. Furthermore, lipopeptide 3163 conjugated gold nanoparticles showed enhanced anti-biofilm activity for both inhibitions of biofilm formation, and eradication of preformed biofilms of Staphylococcus aureus. (S. aureus), E. coli and P. aeruginosa. Interaction between the cell wall of bacteria and desired compound were studied using scanning electron microscopy (SEM) and zeta potential measurement. SEM and zeta potential measurements of the lipopeptide conjugated AuNPs revealed that the membrane lytic mechanism of action was preserved. Lipopeptide 3163 conjugated gold nanoparticles were found to be not hemolytic below 1 mM. Finally, the results gathered from this thesis shows lipopeptide-nanoparticles may have tremendous potential to develop as antimicrobial therapeutics.