Mycobacterium tuberculosis. False-colour TEM of the bacterium Mycobacterium tuberculosis (gold, elongated), the cause of tuberculosis (T. B. ) in humans, within a macrophage. M. tuberculosis is inhaled into the lungs as airborne droplets to form a primary tubercle, an initial focus of infection; spread takes place via adjacent lymph nodes. This form is called pulmonary tuberculosis or consumption (wasting). Phagocytosis (engulfment & digestion) by scavenging macrophages within the lung is part of the body's primary immune response. Magnification: x10,000 at 6x7cm size.