Molecular mechanisms of antibiotic tolerance in mycobacteria
File(s)
Author(s)
Majstorovic, Andrea
Type
Thesis
Abstract
Antimicrobial resistance (AMR) is a critical global health issue requiring comprehensive research to understand its underlying mechanisms and to provide mitigation strategies. AMR can manifest as bacterial growth in the presence of an antibiotic, leading to an increase in the concentration of antibiotic required to inhibit bacterial growth (resistance), or as an ability of a subpopulation (persistence) or a whole population (tolerance) to transiently withstand otherwise lethal concentrations of a drug. Both tolerance and persistence complicate the treatment of many bacterial infections, including tuberculosis; they prolong treatment, lead to treatment failure and disease recurrence, and foster the emergence of resistance. Thus, targeting tolerant and persistent cells would improve treatment outcomes, yet the molecular mechanisms underlying tolerance and persistence remain elusive.
To study the mechanisms behind the development of tolerant and persistent mycobacteria, the Vaubourgeix laboratory developed a method to isolate mutants that display tolerance or high persistence. The lab applied this method to Mycobacterium smegmatis, and isolated 30 mutants that displayed tolerance and/or high persistence upon exposure to kanamycin. My thesis consists of studying two of these mutants, which contain mutations related to a gene encoding a tRNA m1A58 methyltransferase MsTrmI. I found that these mutants display increased survival to aminoglycosides and resistance to macrolides because of a lack of tRNA A58 methylation. I identified that both resistance and tolerance are mediated by increased expression of a transcriptional regulator whiB7. Finally, I proposed a potential mechanism by which whiB7 expression could be maintained during exposure to ribosome-inhibitory antibiotics despite the deployment of rescue mechanisms antagonistic to whiB7 expression. Understanding bacterial resilience to exposure to antibiotics will have implications for developing new antibacterials to be combined with existing drugs. Such combinations would have the potential to shorten treatment, curb the rate of infection relapse and the emergence of resistance.
To study the mechanisms behind the development of tolerant and persistent mycobacteria, the Vaubourgeix laboratory developed a method to isolate mutants that display tolerance or high persistence. The lab applied this method to Mycobacterium smegmatis, and isolated 30 mutants that displayed tolerance and/or high persistence upon exposure to kanamycin. My thesis consists of studying two of these mutants, which contain mutations related to a gene encoding a tRNA m1A58 methyltransferase MsTrmI. I found that these mutants display increased survival to aminoglycosides and resistance to macrolides because of a lack of tRNA A58 methylation. I identified that both resistance and tolerance are mediated by increased expression of a transcriptional regulator whiB7. Finally, I proposed a potential mechanism by which whiB7 expression could be maintained during exposure to ribosome-inhibitory antibiotics despite the deployment of rescue mechanisms antagonistic to whiB7 expression. Understanding bacterial resilience to exposure to antibiotics will have implications for developing new antibacterials to be combined with existing drugs. Such combinations would have the potential to shorten treatment, curb the rate of infection relapse and the emergence of resistance.
Version
Open Access
Date Issued
2023-12-22
Date Awarded
2024-03-01
Copyright Statement
Attribution-NonCommercial 4.0 International Licence (CC BY-NC)
License URL
Advisor
Vaubourgeix, Julien
Holden, David
Sponsor
Department of Infectious Disease at Imperial College London
Publisher Department
Department of Infectious Disease
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)