Color-enhanced, negatively-stained Transmission Electron Micrograph (TEM) of the cell wall of Mycobacterium tuberculosis, showing fibrous structures (mycolic acids) which are responsible for acid-fast reaction, the most distinctive property of the genus. Numerous pit or hole structures are also visible. M. tuberculosis is the causative agent of tuberculosis in humans. Magnification: 83,000x at 70mm.