M. tuberculosis

Mycobacterium tuberculosis is a species of pathogenic bacteria in the family Mycobacteriaceae and the causative agent of tuberculosis. 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, culture, and polymerase chain reaction. Humans are the only known reservoirs of M. tuberculosis. When in the lungs, M. tuberculosis is phagocytosed by alveolar macrophages, but they are unable to kill and digest the bacterium. Its cell wall prevents the fusion of the phagosome with the lysosome, which contains a host of antibacterial factors. The BCG vaccine, derived from M. bovis, has had limited success in preventing tuberculosis.