Ultrathin section of actively growing Mycobacterium tuberculosis showing the filamentous DNA area and dense cytoplasm containing mesosomes and fat granules. They have a relatively thin layer of peptidoglycan compared with other Gram-positive bacteria, but posses and electron translucent external layer, rich in fatty materials, more noticeable between adjacent cells. M. tuberculosis is the causative agent of tuberculosis in humans, a disease characterized by inflammatory infiltrations, formation of tubercles, caseation, necrosis, abscesses, fibrosis and calcification. It most commonly affects the respiratory system, but other parts of the body including gastrintestinal and genitourinary tracts, bones, joints, nervous system, lymph noes and skin may become affected. Infection is usually acquired through contact with an infected person, oan infected cow, or through drinking contaminated milk. TEM Magnification = x4,000 at 70mm