Mycobacterial infection.

Tuberculosis and leprosy are two well known mankind diseases that are caused by members of the genus Mycobacterium. When originally named in 1896, this genus contained the leprosy bacillus (Mycobacterium leprae) observed by Armour Hansen in 1874 and the tubercle bacillus (Mycobacterium tuberculosis) observed and cultured by Robert Koch in 1882. As time went by, other bacilli similar to those of Koch's tubercle bacilli were isolated from various sources mostly from various animals. One of the common properties shared by these organisms is the characteristic staining reaction. They have the ability to resist decolorization in the presence of a weak mineral acid after being stained with an arylmethane dye (acid-fastness). Presently, the genus is defined more precisely on the basis of its antigenic structure and cell wall chemistry, particularly by the length of the carbon chains in long chain fatty-acids, termed mycolic acids. From the purely clinical point of view, mycobacteria are divisable into 3 groups (Grange and Collins, 1983). These are: (1) the obligate pathogens M. tuberculosis and M. leprae, (2) species that normally live freely in the environment but also cause 'opportunistic' infections in man. This group have been referred to by many names such as 'anonymous, atypical, non-tuberculous and mycobacteria other than tubercle (MOTT), and (3) species that never, or with extreme rarity, cause disease, such as M. paratuberculosis and M. lepramurium.