| Popis: |
Antimicrobial lipids such as fatty acids and monoglycerides are promising antibacterial agents that destabilize bacterial cell membranes, representing a new treatment approach that might overcome the challenges of antibiotic-resistant bacteria. To date, most studies on antimicrobial lipids have focused on evaluating inhibitory activity against target bacterium by indirect biological methods. While it is known that antimicrobial lipids act against bacterial cell membranes, it remains to be understood how antimicrobial lipids interact with phospholipid membranes. In this thesis, the objective is to develop a comprehensive physicochemical understanding of how fatty acids and monoglycerides interact with model phospholipid membranes, within the broader context of establishing an experimental framework based on supported lipid bilayers (SLBs) to correlate the molecular self-assembly of antimicrobial lipids with their corresponding biophysical and biological activities. The overall hypothesis of this thesis is that SLB platforms can provide a predictive model system to evaluate the potency and mechanism of action of antimicrobial lipids. To test this hypothesis, a fluid-phase, zwitterionic phospholipid SLB platform was established to investigate the membrane morphological responses induced by antimicrobial lipids, and surface-sensitive measurement techniques revealed that fatty acids promote tubule formation while monoglycerides induce membrane budding. Concentration-dependent trends in membrane-disruptive behavior were observed and correlated with the extent of inhibitory activity against Staphylococcus aureus. It was further determined that fatty acids induce tubule formation and increase membrane fluidity only at or above the corresponding critical micelle concentration (CMC) value, while monoglycerides exhibit dual-mode behavior by inducing membrane budding at or above CMC and promoting tubule formation at lower concentrations. In both cases, monoglycerides also increase membrane fluidity. By taking advantage of new SLB fabrication methods, it was also possible to study the interaction of fatty acids and monoglycerides with cholesterol-containing SLBs across different membrane phase states. Depending on the type of induced membrane morphological response, it was found that cholesterol either inhibited or promoted membrane remodeling in a manner consistent with how cholesterol affects the material properties of phospholipid/cholesterol lipid bilayers. The experimental observations were rationalized by taking into account the chemical structure and self-assembly properties of antimicrobial lipids along with how these molecular characteristics influence membrane translocation and membrane strain in phospholipid membranes. In summary, the findings presented in this thesis demonstrate how SLB platforms can provide a predictive materials science tool for studying antimicrobial lipids, and offer a broadly applicable, integrated experimental approach to characterize the potency and mechanism of action of particular antimicrobial lipids. Doctor of Philosophy |
