{"type":"root","children":[{"type":"paragraph","children":[{"type":"text","value":"Mycobacterium tuberculosis is a pathogenic bacterial species of the Mycobacteriaceae family and the causative agent of most cases of tuberculosis. 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. M. tuberculosis is highly aerobic and requires high levels of oxygen. Humans are the only known reservoirs of this bacteria. When in the lungs, M. tuberculosis is taken up by alveolar macrophages, but they are unable to digest and eradicate the bacterium. Its cell wall prevents the fusion of the phagosome with lysosome, which contains a host of antimycobacterial factors. Antibiotic resistant strains of Mycobacterium tuberculosis have developed resistance to more than one TB drug, due to mutations in their genes."}]}]}