In most forms of the disease, the bacillus spreads slowly and widely in the lungs, causing the formation of hard nodules (tubercles) or large cheeselike masses that break down the respiratory tissues and form cavities in the lungs.

Where is Mycobacterium tuberculosis commonly found?

Tuberculosis (TB) is an acute or chronic bacterial infection found most commonly in the lungs. The infection is spread like a cold, mainly through airborne droplets breathed into the air by a person infected with TB. The bacteria causes formation of small tissue masses called tubercles.

How is tubercle bacilli transmitted?

Infectious droplet nuclei are generated when persons who have pulmonary or laryngeal TB disease cough, sneeze, shout, or sing. TB is spread from person to person through the air. The dots in the air represent droplet nuclei containing tubercle bacilli.