These are Gram-positive, non-sporing acid fast straight or slightly curved bacilli. They are non-motile and range in size between 0.2-0.6 x 1.0-10 mµ). Both branching and mycelium-like growth may occur. They are generally aerobes and produce catalase. Many species form white or creamy coloured colonies but some form bright yellow or orange colonies based on carotenoid pigments, in some cases only as a response to light. They can utilise a wide range of carbon compounds. Glycerol is utilised by all cultivable mycobacteria as sole source of carbon and energy, thus media conating this substrate will grow most species. There may also be a requirement for additional CO2 particularly for clinical isolates. There is only one genus in this family; Mycobacterium. Recent studies based on 16S rRNA analyses have suggested that the family Mycobacteriaceae should include the three genera: Mycobacterium, Nocardia, Rhodococcus.

The Genus

Mycobacterium: On the basis of growth rate, this includes two groups of species, known as the Slow Growers and the Fast Growers. The Slow Growers tend to be associated with human or animal disease, while the Fast Growers tend to be non-pathogenic. They are widely distributed in soil and some marine environments. Over 300 species have been named. The GC content of the DNA of those mycobacterial species studies varies from 66-71 mol%.

Species Profiles

Mycobacterium tuberculosis

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