Tuberculosis (TB) is a disease caused by a germ. called Mycobacterium tuberculosis that is spread. from person to person through air. TB usually. affects the lungs but can affect other parts of the. body, such as the brain, the kidneys or the spine. When a person with infectious TB coughs or sneez-. es, droplets containing Mycobacterium tuberculosis. are expelled into the air. If another person inhales.