Molecular mechanisms of drug synergy and persistence in Mycobacterium tuberculosis
Creators: name: Xu, Ye
Publisher: name: University of Surrey
Year: 2023

description: Tuberculosis (TB) continues to pose a significant public health challenge as one of the leading
description: causes of infectious diseases from a single infectious pathogen, Mycobacterium tuberculosis
description: (Mtb). The persistence of an drug-tolerant subpopulation, known as drug persisters, within the
description: genetically identical bulk population is a crucial factor contributing to the prolonged survival of
description: Mtb during drug treatment, ultimately impeding the eradication of TB in clinical settings. Drug
description: combinations remain an important and effective strategy for TB treatment. Investigation on
description: synergistic combinations targeting both the bulk population and persisters will be beneficial for
description: TB treatment.<br>
description: <br>
description: This thesis focused on investigating the molecular mechanisms of drug persistence genes via
description: transposon mutagenesis and of synergistic drug combinations using RNA sequencing.
description: Considering the requirement of high-level biosafety labs, posing limitations on TB drug
description: research, this thesis often used an auxotroph strain, Mtb H37Rv mc2
description: 6260 (CL2 Mtb), as the research model. This thesis describes the phenotypic examination using checkerboard
description: minimum inhibitory concentration and long-term time-killing experiments to identify Mtb
description: persistence mutants and synergistic combinations targeting both the bulk population and
description: persisters. Persistence formation was corelated with drugs’ mechanism of actions, as
description: persistence-relevant genes were specific to rifampicin (RIF) and streptomycin (STM). The
description: thesis highlighted the involvement of cell membrane biosynthesis, mycolic acid assembly and
description: lipid degradation in RIF persistence formation, and toxin-antitoxin systems in STM persistence
description: formation. Especially, prpD involved in the methyl citrate cycle and fadE5 for lipid degradation
description: were proven to reduce and increase persisters of RIF and could be potential drug targets.<br>
description: <br>
description: The identification of drug-specific persistence mechanisms for RIF and STM paved the way
description: for exploring bactericidal effects on both the bulk population and persisters in drug
description: combinations targeting at diverse cellular pathways, including isoniazid (INH), RIF,
description: clarithromycin (CLAR) and bedaquiline (BDQ). This study identified the synergistic
description: combinations of INH with CLAR and combination of RIF and BDQ. Our results revealed that
description: the synergy between RIF and BDQ are associated with the overload of toxic compounds,
description: especially copper and methyl citrate intermediate. INH and CLAR induce cell membrane
description: disruption, oxidative phosphorylation interference, and substrate transport alterations, all
description: contributing to synergistic bactericidal effects on persisters.<br>
description: <br>
description: In the effort of exploring novel synergistic combinations, two peptides, LYN1D and LYN3D,
description: exhibited anti-mycobacterial properties and selective synergy with BDQ. Notably, the addition
description: of D-isomers to peptides significantly boosted the antibacterial activity. Transcriptome data
description: suggested that LYN1D/3D and BDQ targeted multiple cellular components, disrupting cell
description: membranes and ribosomes. Moreover, a synergistic response between BDQ and LYN1D/3D
description: on oxidative phosphorylation was identified, resulting in intracellular ATP reduction and lethal
description: bactericidal effects.<br>
description: <br>
description: These findings shed light on the complex molecular mechanisms underlying drug persistence
description: and the potential of synergistic combinations to disrupt Mtb survival strategies and enhance
description: TB treatment outcomes.<br>