Tuberculosis is an infectious bacterial disease caused by Mycobacterium tuberculosis. Very often TB is referred to as tuberculosis bacillus.

HIV and TB 

HIV and TB form a lethal combination, each speeding the other's progress. HIV weakens the immune system. Someone who is HIV-positive and infected with TB bacilli is many times more likely to become sick with TB than someone infected with TB bacilli who is HIV-negative (See Section TB/HIV co-infection).

Drug resistant TB

Until 50 years ago, there were no medicines to cure TB. Typical treatment of TB involves the use of four anti-TB drugs or first line drugs. 

Drug-resistant TB is caused: 
when patients do not take all their medicines regularly for the required period;
because doctors and health workers prescribe the wrong treatment regimens;
or because patients can't get the medicine due to unreliable drug supply.