Dissertation
Contributions of Cell Shape and Conformations of Surface Biopolymers of Multidrug-Resistant Escherichia coli to their Adhesion, Elasticity, Biofilm Formation and Resistance Mechanisms to Ampicillin
Doctor of Philosophy (PhD), Washington State University
01/2019
Handle:
https://hdl.handle.net/2376/109868
Abstract
Bacterial multidrug-resistance (MDR) results in two million infections in the US alone. Treating such infections is difficult due to the complex genetic and phenotypic mechanisms associated with MDR. While genetic mechanisms are well explored in the literature, phenotypic mechanisms are not. As such, phenotypic changes of resistant Escherichia coli strains upon exposure to ampicillin including bacterial dimensions, volume, surface area, roughness, membrane permeability, wettability, bacterial surface biopolymers’ thickness and grafting density, initial cellular adhesion, cellular elasticity and biofilm formation were investigated. To achieve our goal, scanning electron, atomic force, optical and fluorescence microscopies as well as contact angle measurements were performed. Our results indicated that MDR-E. coli resist ampicillin using several mechanisms. Upon exposure to ampicillin at the minimum inhibitory concentration (MIC), A5 cells changed their phenotype from elliptical to spherical, decreased their lengths, surface areas, and adhesion and increased their hydrophobicities. When exposed to ampicillin at 20xMIC, A5 cells decreased their size and thicknesses of surface biopolymer brushes and increased their grafting densities and elasticities. With these changes, interactions of cells with ampicillin are expected to be minimized; allowing them to conserve their energies, adapt a dormancy states and become impermeable to ampicillin. In comparison, D4 and A9 cells treated at MIC for 3 hours elongated their cells, increased their surface roughness, adhesion force, and thicknesses of surface biopolymer brushes and decreased their elasticities and grafting densities. These changes suggest that these cells resist ampicillin by increasing their adhesion and biofilm formation to decrease diffusion of ampicillin. After 8 hours of treatment at MIC, D4 and A9 cells increased their elasticities and impermeabilities to ampicillin. Persister cells of A9 resisted ampicillin through increased roughness, grafting densities, adhesion, and elasticities and reduced surface areas. Finally, H5 cells resisted ampicillin through increased biopolymer brush thickness, adhesion and biofilm formation. In summary, this study points to the importance of considering phenotypic mechanisms of bacterial resistance of antibiotics.
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Details
- Title
- Contributions of Cell Shape and Conformations of Surface Biopolymers of Multidrug-Resistant Escherichia coli to their Adhesion, Elasticity, Biofilm Formation and Resistance Mechanisms to Ampicillin
- Creators
- Samuel Chidiebere Uzoechi
- Contributors
- Nehal I Abu-Lail (Advisor)Bernard Van Wie (Committee Member)Haluk Beyenal (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Voiland College of Engineering and Architecture
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Number of pages
- 290
- Identifiers
- 99900581709301842
- Language
- English
- Resource Type
- Dissertation