Elucidating the antimicrobial mechanisms of colistin on Mycobacterium tuberculosis using metabolomics
In 2014, the WHO declared tuberculosis (TB) an epidemic, as an estimated 9 million people suffered from Mtb infection. Today, millions of mortalities are still reported worldwide as a result of this disease. This growing TB incidence may be ascribed to a variety of reasons, including, treatment failure, poor patient adherence, lack of new anti-TB drugs, and long treatment duration. Despite the wide research on anti-TB drugs to date, the mechanisms of these drugs remain poorly understood. Colistin sulfate (CS) and colistin methanesulfonate (CMS) provide hope for a promising outcome as a new anti-TB drug, however its exact mechanism of action has not been explored. It is also unclear how colistin could provide the necessary treatment advances to the current six-month "directly observed treatment short-course" (DOTS) regimen. Thus, there is a need for new, sensitive and specific analytical techniques to elucidate the anti-bacterial effect of colistin on TB. Considering this, we used GCxGC-TOFMS metabolomics and identified new metabolite markers for the purpose of confirming or elucidating both forms of colistin’s mechanisms of action against Mycobacterium tuberculosis (Mtb). The most significant observations were the unanimous flux in the metabolism of the colistin treated Mtb towards fatty acid synthesis and cell wall repair, confirming previous reports that colistin acts by disrupting the cell wall of mycobacteria. Accompanying this, is a subsequently elevated glucose uptake, since it serves as the primary energy substrate for the upregulated glyoxylate cycle, and additionally as a precursor for further fatty acid synthesis via the glycerolipid metabolic pathway. In addition to the proposal of a number of new hypotheses, explaining various mechanisms of colistin, the mapping of the newly identified metabolite markers led to the confirmation of various previously suggested metabolic pathways and alterations thereof due to an assortment of perturbations. Therefore, this study significantly contributes to the characterisation of colistin, which may in the future lead to a new treatment protocol for TB, pertaining to the global TB epidemic.