Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Biomedical Sciences


Microbiology, Immunology, and Biochemistry

Research Advisor

Richard E. Lee, Ph.D.


Kim Lewis, P. David Rogers, Jason W. Rosch, Elaine I. Tuomanen, Stephen W. White


Antibiotic, Drug discovery, Drug resistance, Gram-negative bacteria, Metabolism, Staphylococcus aureus


Over the last century, the use of antibiotics has enabled many advances in modern medicine, making life as we know it possible. In recent years, however, emerging bacterial resistance to virtually all major antibiotic classes has resulted in a worldwide increase in morbidity, mortality, and financial burden associated with drug resistant infections. The antimicrobial resistance crisis presents an urgent need for new antimicrobials with distinct mechanisms of action from existing drugs. The current pharmaceutical pipeline of new antibiotics is limited due to three obstacles: a lack of understanding of resistance mechanisms, a dearth of novel mechanisms of action among new antibiotics, and drug discovery challenges unique to bacteria due to their cellular and physiological composition. My dissertation research addressed each of these challenges. The mechanisms of resistance to folate biosynthesis inhibitors in Staphylococcus aureus were explored from a genetic, biological, biochemical, and structural basis. Unexpected roles in resistance and fitness were attributed to various mutations in the sulfonamide target dihydropteroate synthase. This information currently guides the development of next-generation antifolates designed to avoid these characterized resistance strategies. In the subsequent chapter, a conditional metabolic screening approach was employed to discover inhibitors disrupting metabolic pathways related to folate biosynthesis. The testing conditions were optimized to measure the biological activity of antimetabolites, which is often masked by nutrients present in standard testing media. This screen yielded an inhibitor of cysteine synthase A in Escherichia coli, which was characterized in chapter four. Multiple experimental approaches yielded indications that the cysteine synthase A inhibitors have a false-product mechanism, resulting in a widespread impact on several key branches of metabolism beyond cysteine biosynthesis. The final research chapter describes the adaptation of the cellular thermal shift assay to explore target engagement in the Gram-negative cell system. Drug entry and accumulation are especially challenging to achieve in Gram-negative cells due to their unique dual membrane system and associated efflux machinery. This assay provided an early stage tool to quickly assess the ability of antimicrobial candidates to engage the intended target in the intact cell system and also measure efflux sensitivity. Taken together, this dissertation contributes to the fight against the antimicrobial resistance crisis from multiple angles, all within the context of bacterial metabolism which is a rich source of exciting new antibiotic targets.

Declaration of Authorship

Declaration of Authorship is included in the supplemental files.