Pulmonary tuberculosis (TB) is a contagious bacterial infection that involves the lungs. It may spread to other organs. Pulmonary tuberculosis (TB) is caused by the bacterium Mycobacterium tuberculosis (M. tuberculosis). TB is contagious. This means the bacteria is easily spread from an infected person to someone else. You can get TB by breathing in air droplets from a cough or sneeze of an infected person. The resulting lung infection is called primary TB.