Chemical Genetic Approaches to understanding mycobacterial pathogenesis
Chronic bacterial infections are a dangerous, worldwide health burden that requires costly and lengthy therapies that in many cases are ultimately ineffective. Chief among these pathogens is Mycobacterium tuberculosis (Mtb), which causes a notoriously persistent infection resulting in 1.8 million deaths worldwide each year. During infection, Mtb is exposed to a decrease in oxygen availability (hypoxia) and responds by forming a subpopulation of non-replicating, drug-tolerant bacteria. These drug-tolerant Mtb are the reason that Mtb can persist within an individual for decades and resist elimination by the host immune system and antibiotics. It is imperative to discover new agents to treat chronic Mtb infections and prevent the formation of antibiotic tolerant populations, which requires insight into the processes involved in drug tolerance. Hypoxia signals numerous changes in Mtb and it is unknown what part of this large and pleiotropic response is responsible for antibiotic tolerance. Using a chemical approach to dissect hypoxia-induced persistence, we have uncovered a change in lipid composition that Mtb undergoes when transitioning to a more drug tolerant state. Compounds that block this developmental change in lipid composition, without interfering with the rest of the hypoxia response, restrain Mtb in a drug-sensitive state where it can be effectively killed by isoniazid. Isoniazid, a key component of anti-tuberculosis therapy, is otherwise ineffective against persistent bacteria. In addition, chemical inhibition of this change in lipid composition also blocks cording (a known virulence characteristic of Mtb), biofilm formation, and tolerance to oxidative stress. Our data reveal a mechanism by which Mtb persisters tolerate isoniazid treatment and oxidative stress as well as a way to break this tolerance.