The evolution of antibiotic-resistant bacteria and their treatment using epoxytigliane-based therapeutics

Wu, Jingxiang 2025. The evolution of antibiotic-resistant bacteria and their treatment using epoxytigliane-based therapeutics. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

The discovery of plasmid-encoded mobile colistin resistance (mcr) genes and their rapid dissemination and persistence in humans, animals and the environment represents a significant global health concern. Understanding the fitness costs conferred by mcr and how these genes are maintained in bacterial populations is crucial for developing effective containment strategies. Epoxytiglianes such as EBCs, a novel class of lipophilic, plant-derived compounds, may hold promise in overcoming mcr-mediated colistin resistance, as previous research has revealed their potential role against antibiotic-resistant, biofilm-associated Gram-negative infections. The phenotypic effects of mcr-1 and mcr-3 carriage on bacterial growth and biofilm assembly were studied. The persistence of both mcr plasmids in E. coli populations in the presence and absence of colistin selective pressure was studied in an evolutionary bead biofilm model and modelled mathematically. Changes in resistance profiles and plasmid genetics were monitored using minimum inhibitory concentration assays and whole genome sequencing. The direct interaction of EBCs with the Gram-negative bacterial cell membrane was studied using in silico simulations, and the induced cell surface chemical changes were characterised in vivo using spectroscopy- and microscopy-based surface chemistry analyses. Bacterial membrane and biofilm disruption after EBC treatment was also examined using bacterial membrane permeability assays and microscopic imaging. iv Phenotypic characterisation demonstrated that both mcr-1 and mcr-3 plasmid carriage were associated with fitness costs, with biofilm-associated characteristics, including formation, mechanics and stress response to colistin, also significantly altered. In the absence of colistin, mcr-1 was rapidly lost (Day 23), but mcr-3 persisted (>51 days). At the end of the evolution experiment, colistin resistance rapidly re-emerged in the apparently mcr-1-depleted biofilm populations upon re-exposure to colistin (in <48 h). Sequencing confirmed maintenance of mcr-1 was associated with deletion of other antimicrobial resistance genes from the plasmid multidrug resistance region. Interaction of EBC-1013 with the bacterial cell membrane was evident in silico and in vivo, with alterations in the membrane lipid and protein compositions, which was reflected in compromised membrane integrity. The marked synergistic effect of EBC-1013 upon colistin activity against mcr E. coli was evident in the biofilm disruption assay. This work highlights the importance of the fitness costs of mcr carriage and describes underlying compensatory mechanisms within the biofilm environment which may maintain carriage of colistin resistance. This study also emphasises the potential value of EBC-1013 as a novel antimicrobial agent that can target mcr-bearing, colistin-resistant bacteria in human disease through its interaction with the bacterial outer membrane and by potentiating the activity of colistin.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Dentistry
Subjects:	Q Science > QR Microbiology R Medicine > RM Therapeutics. Pharmacology
Funders:	QBiotics, Chinese Scholarship Council
Date of First Compliant Deposit:	5 February 2026
Last Modified:	05 Feb 2026 09:17
URI:	https://orca.cardiff.ac.uk/id/eprint/184437

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