Tuberculosis (TB) is caused by the bacterial group known as Mycobacterium tuberculosis complex (e.g., M. tuberculosis, M. bovis, M. africanum, M. microti, M. canetti, M. pinnipedii, M. mungi, M. caprae). Mycobacterium tuberculosis is the most common of this complex to cause TB disease in humans, while the other members of the complex cause diseases similar to TB.
These bacteria may be transmitted from person to person through the air. Coughing or sneezing by individuals infected with active TB disease causes the release of microscopic droplets (containing tubercle bacilli) into the air. Others may then inhale these droplets. TB usually affects the lungs but can also cause infection in the brain, spine, kidneys, and other locations. In pulmonary TB, the tubercle bacilli multiply in the lung's alveoli.
Figure 2. CDC/ V. McPheeters. (1965). This photomicrograph of a Ziehl-Neelsen-stained specimen revealed the presence of magenta stained, rod-shaped, acid-fast, Mycobacterium tuberculosis bacilli. Centers for Disease Control and Prevention Public Health Image Library. https://phil.cdc.gov/Details.aspx?pid=23000
