Inhibiting the stringent response blocks <i>Mycobacterium tuberculosis</i> entry into quiescence and reduces persistence

Abstract

The stringent response enables <i>Mycobacterium tuberculosis</i> (<i>Mtb</i>) to shut down its replication and metabolism under various stresses. Here we show that <i>Mtb</i> lacking the stringent response enzyme Rel_Mtb was unable to slow its replication rate during nutrient starvation. Metabolomics analysis revealed that the nutrient-starved <i>rel_Mtb</i> -deficient strain had increased metabolism similar to that of exponentially growing wild-type bacteria in nutrient-rich broth, consistent with an inability to enter quiescence. Deficiency of <i>rel_Mtb</i> increased the susceptibility of mutant bacteria to killing by isoniazid during nutrient starvation and in the lungs of chronically infected mice. We screened a pharmaceutical library of over 2 million compounds for inhibitors of Rel_Mtb and showed that the lead compound X9 was able to directly kill nutrient-starved <i>M. tuberculosis</i> and enhanced the killing activity of isoniazid. Inhibition of Rel_Mtb is a promising approach to target <i>M. tuberculosis</i> persisters, with the potential to shorten the duration of TB treatment.