Mycobacterium tuberculosis

Mycobacterium tuberculosis are seen as acid-fast bacilli when stained with the Zeihl-Neelsen acid-fast stain and viewed at 1,000X magnification. These bacteria were seen in a sputum sample from a patient with active tuberculosis.

Mycobacterium tuberculosis is an aerobic intracellular pathogen, spread by aerosol droplets. M. tuberculosis is a slow growing organism and it takes weeks to incubate because of the complexity of the cell wall. The bacilli primarily infect the pulmonary system, but can spread to any body site for immunocompromised patients. M. tuberculosis bacilli inhabit unactivated macrophage in the alveoli (1). Patchy infiltrates form when the bacilli grow unchecked. Active tuberculosis is characterized by a continual cough, weight loss, night sweats and the presence of acid-fast bacilli in sputum.

Mycobacteria contain mycolic acids and have a high GC content in their DNA. A Gram stain cannot penetrate the waxy cell wall. The hydrophobic lipids cause the Gram stain to give no staining or a variable result. An acid-fast stain is used to visualize the bacilli. Mycobacteria are referred to as acid fast because they retain the acid-fast dye, Carbolfusion the primary stain of the acid fast procedure. As seen in the image the cells stain bright pink with this procedure.

The mycolic acids are comprised of free lipids, glycolipids and peptidoglycolipids. The host