Date of Award

5-11-2025

Date Published

June 2025

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Advisor(s)

YanYeung Luk

Keywords

Antibiotic resistance;Beta-lactam;Beta-lactamase;Chromosomal mutations;Grignard Reaction;Horizontal Gene Transfer

Subject Categories

Chemistry | Physical Sciences and Mathematics

Abstract

The emergence of antibiotic resistance poses a significant threat to global health, with certain bacterial strains evolving to resist multiple drugs. Urgent action is necessary to develop new antibacterial agents that effectively target these resistant strains; however, no new classes of antibiotics have been approved in recent decades. This research employs innovative biological tools to identify and highlight factors influencing resistance dynamics. Additionally, this study refines the novel approach by utilizing adjuvants to chemically repurpose existing antibiotics and improve their effectiveness against antibiotic-resistant strains. Pseudomonas aeruginosa, recognized for its adaptability, persistent infections—especially in cystic fibrosis patients—and widespread antibiotic resistance, serves as our model organism. Horizontal gene transfer (HGT) is the exchange of genes between related and distinct species and represents the primary mechanism by which resistance spreads in bacteria. While the scientific community accepts that HGT contributes to resistance development, the magnitude and extent of this contribution remain open questions. In this work, we design novel serial passage assays on agar to highlight and quantify the effects of HGT during resistance development. We demonstrate that strains stressed in the presence of HGT with a single antibiotic (a beta-lactam) achieve high-level resistance (extremely high MICs), display increased fitness, and develop resistance to other antibiotics (multi-drug resistance (MDR)). Additionally, our work shows that strains stressed with one antibiotic without HGT can become resistant to that antibiotic, but exhibit increased susceptibility to other antibiotics compared to wild types, a phenomenon termed hyper-susceptibility. This study provides experimental evidence that horizontal gene transfer contributes to multi-drug resistance and the emergence of superbugs. Therefore, HGT should be considered and addressed when developing strategies against the rise of MDR strains. The Luk Lab's recent work has introduced a new class of small molecule ligands that bind to two essential proteins—LecA and Pili—thus inhibiting tolerance, a precursor to resistance in Pseudomonas aeruginosa. We are investigating how these ligands can control horizontal gene transfer (HGT) and resistance. This research employs a small ligand molecule, SFβC, to inhibit and reverse resistance in wild-type PAO1. SFβC inhibited the development of Aztreonam resistance in PAO1 over 20 days by lowering the minimum inhibitory concentration (MIC). Furthermore, this study demonstrates that SFβC can reverse acquired resistance once it has developed, sometimes reducing the MIC to below initial susceptible levels in systems where HGT is blocked. In growth rate curves, this research indicates that SFβC enhances and allows sub-MIC concentrations of Aztreonam to kill Aztreonam-resistant strains. Bacteria have developed numerous strategies to evade treatment beyond resistance, including biofilm formation, tolerance, and persistence. Biofilms protect bacteria by limiting antibiotic penetration and as a hub for tolerant and persistent strains. Most conventional antibiotics promote biofilm formation and tolerance at sub-lethal concentrations. However, the Luk lab has introduced a new antibiotic, Farnesol Triazole Cellobioside (FTC), effectively kills bacteria without promoting tolerance and persistence. This research demonstrates that sub-MIC concentrations of FTC inhibit biofilm formation while conventional antibiotics promote it. Furthermore, this study reports progress in synthesizing a potential new antibiotic, 3,3-diMeTC, featuring 3,3-dimethyl branching based on structural modifications of FTC to achieve lower MICs against gram-negative bacteria. Collectively, this research presents promising strategies in the fight against antibiotic resistance by proposing methods to understand and inhibit resistance and designing new antibacterial agents to target resistant strains effectively.

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Open Access

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Chemistry Commons

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