Mycobacterium tuberculosis (MTB) is a pathogenic bacterial species in the genus Mycobacterium and the causative agent of most cases of tuberculosis. M. tuberculosis has an unusual, waxy coating on the cell surface (primarily mycolic acid), which makes the cells impervious to Gram staining so acid-fast detection techniques are used instead. ESAT-6, the 6 kDa early secretory antigenic target of Mycobacterium tuberculosis, is a secretory protein and potent T cell antigen. It is used in tuberculosis diagnosis by the whole blood interferon gamma test QuantiFERON-TB Gold, in conjunction with CFP-10 and TB7.7. . Alternative Names: ESAT 6 protein, Mycobacterium Tuberculosis ESAT6 protein, ESAT6 protein, TB ESAT6 protein