Phenotypic discrimination of Mycobacterium tuberculosis by Raman spectroscopy

TB remains a major health issue worldwide causing around 1.5 deaths each year. The recent phase III clinical trials of shortened TB treatment failed to show superiority compared to the current regimen and this mainly because of relapse. Relapse is thought to be caused by dormant bacteria. Dormancy in Mycobacterium species has been shown to be associated with the accumulation of intracellular lipids, defining two phenotypes: the lipid rich (LR) cells (associated with dormancy) and the lipid poor (LP) cells (non-dormant). LR cells were shown to have a higher phenotypic antibiotic resistance compared to LP cells. Studying these two phenotypes is therefore central in tuberculosis research to understand better the disease and also potentially start to reveal the bacteriology of relapse. We investigated the power of Raman spectroscopy, a label-free and non-destructive technique, to discriminate LR and LP bacteria both in-vitro and ex-vivo. This represents the first Raman spectroscopy study that tries to discriminate the phenotypes of M. tuberculosis and investigate them directly at the site of the disease. Using total lipid extract of M. tuberculosis, we showed the location of the main lipid bands in the Raman spectrum. ... (continues)