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Title: Role of bacterial lipocalin proteins in antimicrobial resistance
Author: Mohamed Naguib Mohamed Shoukry Khobaz, Marwa
ISNI:       0000 0004 7971 8815
Awarding Body: Queen's University Belfast
Current Institution: Queen's University Belfast
Date of Award: 2019
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Burkholderia cenocepacia, an opportunistic Gram-negative bacterium that causes serious respiratory infections in patients with cystic fibrosis, produces the extracellular bacterial lipocalin protein BcnA upon exposure to sublethal concentrations of bactericidal antibiotics. BcnA captures a range of antibiotics outside bacterial cells, providing a global extracellular mechanism of antimicrobial resistance. In this thesis, I report that watersoluble and liposoluble forms of vitamin E inhibit antibiotic binding by BcnA. In vitro, both vitamin E forms bind strongly to BcnA and contribute to reduce the MICs of antibiotics. Expression of BcnA was required for the adjuvant effect of vitamin E. In vivo, vitamin E and norfloxacin treatment significantly increased Galleria mellonella larva survival upon infection in a BcnAdependent manner. Together, my findings suggest that vitamin E can be used to increase killing by bactericidal antibiotics through interference with lipocalin binding. The transcription of bcnA gene increases upon antibiotic stress, which stimulates the oxidative stress and membrane lipid peroxidation. BcnA lipocalin, and associated proteins BcoA cytochrome and BarA reductase are involved in membrane peroxidation stress response to antibiotics and other forms of oxidative stress. I report that bcnA, bcoA and barA deletion mutants display enhanced membrane lipid peroxidation and fail to survive under conditions that stimulate peroxidative stress (e.g. Tellurite treatment, cold stress and salt stress). Peroxidation also affects the functionality of the bacterial outer membrane. Absence of BcnA compromises the permeability of the outer membrane, resulting in the release of extracellular DNA leading to a depletion aggregation phenotype and cell death. Together, my findings uncover a novel peroxidation quenching mechanism based on B. cenocepacia BcnA, BcoA and BarA, which protects the bacterial cell envelope against lipid peroxidation stimulated by antibiotic or metal stress, in the presence of oxygen.
Supervisor: Valvano, Miguel Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Antibiotic intrinsic resistance ; Bactericidal antibiotics ; Burkholderia cenocepacia ; Cystic fibrosis ; Lipocalins ; Oxidative stress ; Reactive oxygen species ; Cytochrome b-561 ; Aldehyde reductase ; Outer membrane permeability ; Vitamin E