The assessment of changes to the nontuberculous mycobacterial metabolome in response to anti-TB drugs

Mycobacterium species can cause a range of nontuberculous infections of healthy and immunocompromised people as well as infected people during and after surgical procedures. The similarity of nontuberculous mycobacteria (NTM) to the tuberculosis bacilli (TB) could ultimately enable the use of anti-TB drugs for the genus. Hence, three NTM (Mycobacterium smegmatis, Mycobacterium phlei and Mycobacterium avium) were cultured under different lab conditions, causing two mycobacterial phenotypes (active and dormant), and treated with isoniazid (INH) and ethambutol (EMB) independently or in combination. Metabolite profiling was applied to facilitate the investigation and characterisation of intracellular targets affected by the antibiotics. Aliquots of the cell culture were taken over the treatment period and the metabolite profile of the cells analysed by gas chromatography mass spectrometry. Comparative analysis of the metabolite levels to untreated mycobacteria confirmed the successful action of the antibiotics on the metabolism of all three species. Furthermore, single metabolites and metabolite pathways affected by the antibiotics could be identified and included, besides the known target sites for INH and EMB on mycobacterial cells, changes in e.g. nucleotide and saccharide levels. The combined treatment highlighted the property of EMB to enhance the effects of INH even under hypoxic culture conditions.