The lysosome is the organelle most directly affected by tuberculosis (TB) infection. Mycobacterium tuberculosis, the bacterium that causes TB, infects macrophages (a type of immune cell) and survives inside them by interfering with the normal function of lysosomes. Specifically, the bacterium prevents the fusion of the phagosome (the vesicle that engulfs the bacterium) with the lysosome. This allows the bacteria to evade degradation by the lysosome’s hydrolytic enzymes, enabling it to persist and replicate within the host cells.