ESX1 and infection: We found that there were more genes functioning in the stress response down-regulated in the intracellular MKR superspreader compared to that of H37Rv, and more interestingly, we found that the cholesterol degradation pathway and the ESX-1 virulence molecule secretion system appeared to be up-regulated overall in the MRK superspreader after the host cell infection, but not in H37Rv.