Evaluating Mycobacterium komossense JERR01 as a possible model organism for Mycobacterium tuberculosis antibiotic resistance studies

Abstract

Multi-drug-resistant tuberculosis (MDR-TB) accounted for an estimated 410,000 cases of all TB infections in 2022 and presents a major challenge for global health. Studying TB is complicated due to the fastidiousness and high pathogenicity of Mycobacterium tuberculosis (Mtb) that requires specialized facilities, expensive equipment, and long experimentation phases. To overcome these challenges, various Mycobacterium species have been developed as model organisms that share some of the characteristics of Mtb but are less pathogenic and more amenable to experimentation have been proposed in the past. All these models have limitations, therefore new models for Mtb that better replicate properties of the pathogen are needed.

This thesis investigates a mycobacterial strain, JERR01, that was originally identified as Mycobacterium komossense as a model organism for the development of antimicrobial resistance (AMR) towards key drugs used for the treatment of TB. Through initial phenotypic characterization of the strain that originated from a human urine sample, it was determined that this strain was fast-growing and shared similar antibiotic sensitivity profiles to Mtb for six antitubercular drugs, suggesting suitability for studying AMR development. Genomic characterisation of the strain and comparison to a type strain of M. komossense revealed that its original taxonomic designation was imprecise. Wider comparison genomic analyses provided evidence that JERR01 belonged to the Fortuitum-Vaccae clade of Mycobacterium but designated it as an unclassified mycobacterial species. Having identified homologs of genes associated with resistance to antitubercular drugs in M. JERR01, in vitro studies were conducted to see how resistance to rifampicin and isoniazid, two key drugs used in tuberculosis treatment, could evolve through in vitro experimentation. For rifampicin, similar mutational pathways to Mtb were identified in the rpoB gene, the primary target of resistance. The mutations associated with decreased sensitivity to isoniazid were almost exclusively associated with inactivating katG, which encodes the gene catalase-peroxidase responsible for activating the pro-drug isoniazid. This contrasts to the mutational pathways for isoniazid in Mtb which encompass a broader range of loci and mutations. Overall, this work has identified a mycobacterial strain that can safely and rapidly grow in the laboratory to investigate the development of resistance to antituberculosis drugs and has the potential to act as a model organism for studying AMR in Mtb.

Date of Award	Jul 2025
Original language	English
Awarding Institution	University of St Andrews
Supervisor	Matthew Holden (Supervisor), Andreas Haag (Supervisor) & Derek James Sloan (Supervisor)