Sarah Schmidt Grant
Brigham and Womens Hospital, USA
Sarah Grant is a physician-scientist at the Brigham and Women’s Hospital and the Broad Institute of MIT and Harvard. She currently is completing a post-doctoral fellowship with Dr. Deborah Hung at the Broad Institute, using chemical genetics to study the physiology of the non-replicating M. tuberculosis bacilli.
During both active and latent infection, a subpopulation of Mycobacterium tuberculosis bacteria likely exists in a non-replicating, metabolically inactive state. The presence of non-replicating bacteria within the host likely contributes to the need for prolonged drug therapy for active and latent M. tuberculosis infection. A better understanding of the non-replicating state may lead to the development of new antibiotic therapies targeting essential processes in the non-replicating M. tuberculosis bacterium. Here we describe a chemical genetic approach to identify small molecules that affect the viability of non-replicating M. tuberculosis. A carbon starvation assay was used to model non-replicating, antibiotic tolerant M. tuberculosis. 23,680 compounds were screened in duplicate against carbon-starved M. tuberculosis and 308 compounds were identified as hits. Whole genome sequencing was used to identify bacterial mechanisms of resistance for 6 chemical scaffolds. For one scaffold, named compound 5849, resistance is mediated by single nucleotide polymorphisms (SNPs) in a transcriptional regulator. Gene expression profiling suggests that this regulator may represent a novel regulator of mycolic acid synthesis. Biochemical experiments with compound 5849 confirm mycolic acid inhibition. The mechanism of action for this compound suggests a role for mycolic acid synthesis and/or modification in the non-replicating state.