Investigating the response of Mycobacterium tuberculosis to anti-tuberculosis drugs

Abstract

Following the introduction of streptomycin in 1947, the main issue for new drug treatments has been to avoid drug resistance. This has been achieved, in part, by identifying the most effective drug combinations. Conventional methods used for testing combinations of current and new drug regimens and the response of M. tuberculosis to treatment are complicated and time consuming. Other issues include the need for accurate and early detection, drug resistance screening and follow-up measures to ensure treatment completion as intended. Thus, there is an urgent need to develop robust and rapid tools to assess drug efficacy and measure the response to treatment. The main scope of this thesis is to understand current available methods to predict the action of novel drugs in combination, and to determine drug responses to inform/improve patient management. Therefore, I evaluated the Molecular Bacterial Load (MBL) assay as a tool for diagnosis of M. tuberculosis and monitoring treatment response. This has confirmed that the MBL assay is a faster and more sensitive approach compared to culture-based methods. I then investigated the interaction between anti-tuberculosis drugs in vitro, and determined the transcriptomic profile of 16 key genes in response to drugs such as rifampicin (the backbone of treatment for TB), para-amino salicylic acid (PAS) (used in the treatment of MDR TB) and bedaquiline (a new drug increasingly used worldwide, which acts on persister type of bacilli). I also performed phenotypic synergism studies using these drugs. Both approaches demonstrated an antagonistic interaction between rifampicin, PAS and bedaquiline in different physiological states. Finally, the utility of whole-genome sequencing (WGS) in tracking the evolution of drug resistance was evaluated in comparison to conventional phenotypic DST profiles in clinical isolates. This confirmed a good correlation between these methods. My WGS work identified uncommon mutations associated with resistance to isoniazid and moxifloxacin which had been only rarely reported prior to this in the literature.