*Mycobacteruim organisms belong to the family Mycobacteriaceae, order Actinomycetales. This class of organism includes obligate pathogens, opportunistic pathogens and saprophytes; they can cause chronic, progressive, granulomatous infections including tuberculosis, Johne's disease and feline leprosy. M. bovis, M. tuberculosis and M. avium cause tuberculosis of cattle, tuberculosis of pigs and tuberculosis of dogs respectively. Mycobacterium leprae and M.lepraemurium cause human, feline/murine leprosy respectively. Localized opportunistic skin and subcutaneous infection can be caused by saprophytic and rapidly growing atypical mycobacteria.
Environmental species are found in soil, vegetation and water. Mycobacterium organisms are non-motile, non-spore forming weakly Gram-positive acid-fast rods. They require egg-based media for growth, forming slow-growing (three weeks are required for culture) colonies that stain with carbol dyes and resist subsequent decolorization with inorganic acids; this characteristic which is due to the spatial arrangement of mycolic acids within the cell wall makes them acid fast. They are identified by Ziehl-Neelson staining and differentiated by culture, biochemical tests, chromatography and molecular techniques.Mycobacterium species are resistant to disinfectants and environmental conditions, but are susceptible to pasteurisation.