Causative agent of T.B is
Mycobacterium
Tuberculosis(T.B) is an infectious disease usually caused by Mycobacterium tuberculosis. Tuberculosis generally affects the lungs, but can also affect other parts of the body
Most people infected with the bacteria that cause tuberculosis don't have symptoms. When symptoms do occur, they usually include a cough (sometimes blood-tinged), weight loss, night sweats and fever.
Hence causative agent of T.B is Mycobacterium.
So, the correct answer is 'Mycobacterium'.