Mtb encounters a vastly changed environment, soon after it gets internalized by macrophages. The compartment it resides in, the phagosome, is acidified and devoid of important metal ions. It is flooded with reactive oxygen and nitrogen species. And steps will be soon taken by the macrophage to "mature" the phagosome with all kinds of lysosomal digestive enzymes. However, unlike most other bacteria species Mtb. has evolved solutions to each of these threats and, after making sure these are installed, it soon will enter a dormant state (de Chastellier, 2009; Flannagan et al, 2009). A combination of the host defense and the response of the infecting bacillus (active and passive) ensure suppression of bacterial metabolic activity and replication, resulting in a non-replicating state (Russell 2011, Russell et al. 2010).