Dai, Hai-LungWillets, Katherine A.2024-06-052024-06-052024-05http://hdl.handle.net/20.500.12613/10287Molecular efflux is a process through which bacteria actively expel unwanted substances to ensure their survival. For strains of bacteria equipped with efflux pumps, this mechanism serves as a major defense against toxic compounds in harsh environments. Understanding how molecular efflux works is crucial for dealing with undesirable bacteria issues, such as biodegradation in fuel tanks. Although much has been learned about the structure and functions of molecular efflux, the specifics of its mechanism—particularly from which parts of the bacteria efflux pumps eject undesirable molecules and the associated ejection rates—have yet to be determined for any efflux system. This thesis embarks on an in-depth exploration of the bacterial efflux mechanisms and the interactions with their inhibitors through the application of the second harmonic scattering(SHS) technique. The research is segmented into three integral parts, each shedding light on different facets of bacterial resistance and the potential avenues for overcoming it.The first section delves into the dynamics of molecular efflux in Pseudomonas aeruginosa, particularly focusing on the efflux rates of the antimicrobial agent malachite green (MG). Utilizing SHS, the study quantitatively measures how an SH active molecule, MG, is expelled from each compartment of the bacterial cytoplasmic membrane, revealing the efflux pump is activated at high concentration condition. It also quantitatively evaluates how an SH inactive molecule, hexane which is another effluxable compound, significantly impacts the efficacy of MG efflux by competing for the efflux pathway, providing insights into the survival of bacteria in alkane – environment, such as the fuel tank. This knowledge helps us know that the function of the efflux pump is substantially important in reducing the accumulation of the bad molecules. The second part of the thesis examines the impact of phenylalanine-arginine beta-naphthylamide (PAβN) on the efflux mechanisms of P. aeruginosa, particularly its role in inhibiting the bacteria's ability to expel substances. While it's established that PAβN can hinder these efflux pumps, the exact manner in which it does so remains somewhat obscure. This ambiguity arises because the process by which PAβN traverses the bacterial membrane—essential for its interaction with the efflux pumps—is well understood, yet its direct effects on the functioning of these pumps require further clarification. Through SHS, the study indirectly observes PAβN's transport across bacterial membranes and its interaction with internal pump proteins, underscoring its inhibitory effect on efflux pumps. Moreover, the research uncovers an unintended increase in membrane permeability caused by PAβN, highlighting the intricate balance between inhibitory effectiveness and potential adverse effects, which is crucial for the development of efflux pump inhibitors as therapeutic agents. The final part investigates the adsorption of small molecules at the heterogeneous solid-liquid interface, a critical process in drug delivery and bacterial membrane interaction. Through SHS and comprehensive simulations, the study elucidates that SHS technique is sensitive to the multisite adsorption mechanisms.177 pagesengIN COPYRIGHT- This Rights Statement can be used for an Item that is in copyright. Using this statement implies that the organization making this Item available has determined that the Item is in copyright and either is the rights-holder, has obtained permission from the rights-holder(s) to make their Work(s) available, or makes the Item available under an exception or limitation to copyright (including Fair Use) that entitles it to make the Item available.http://rightsstatements.org/vocab/InC/1.0/Physical chemistryBiochemistryText151382024-05-24Li_temple_0225E_15138.pdf