Micrograph of tubercular granuloma in the lung. Tuberculosis (TB) is a common, often deadly disease caused by the bacteria Mycobacterium tuberculosis. It usually attacks the lungs (pulmonary TB), but can also infect the central nervous; lymphatic; circulatory; genitourinary; and gastrointestinal systems. It can also impact the bones, joints, and sometimes the skin. Tuberculosis is classified as one of the granulomatous inflammatory conditions.