Bacteria that cause disease rely on their ability to counteract and overcome host defenses. Here we present a genome-scale study of Mycobacterium tuberculosis (Mtb) that uncovers the bacterial determinants of surviving host immunity, sets of genes we term “counteractomes.” Through this, we find that CD4 T cells attempt to starve Mtb of tryptophan through a mechanism that limits Chlamydia and Leishmania infections. In those cases, tryptophan starvation works well, since those pathogens are natural tryptophan auxotrophs. Mtb, however, can synthesize tryptophan, and thus starvation fails as an Mtb-killing mechanism. We then describe a small molecule inhibitor of Mtb tryptophan synthesis, which turns Mtb into a tryptophan auxotroph and restores the efficacy of a failed host defense. Together, our findings demonstrate that the Mtb determinants for surviving host immunity—Mtb’s immune counteractomes—serve as probes of host immunity, uncovering immune-mediated stresses that can be leveraged for therapeutic discovery.