Mycobacterium tuberculosis is an obligate
pathogenic bacterial species in the family
Mycobacteriaceae and the causative agent of most cases of
tuberculosis. First discovered in 1882 by
Robert Koch,
M. tuberculosis has an unusual, waxy coating on its cell surface (primarily due to the presence of
mycolic acid), which makes the cells impervious to
Gram staining;
M. tuberculosis can appear Gram negative and Gram positive in clinical settings. The
Ziehl-Neelsen stain, or acid-fast stain, is used instead. The physiology of
M. tuberculosis is highly
aerobic and requires high levels of oxygen. Primarily a pathogen of the mammalian
respiratory system, it infects the lungs. The most frequently used diagnostic methods for tuberculosis are the tuberculin skin test, acid-fast stain, and chest radiographs.