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• Obligate aerobes.
• Short, thin rods or fragile filaments.
• 0.2-0.8 x 1-10 (rods) um in size.
• Non- motile.
• Cells stain Gram positive.
• Typically chemoorganoheterotrophic, though some strains may be chemolithotrophic.
• The percent G + C ranges from 62-70%.
• Some strains pigmented.
• Notorious for their slow growth rate.
• Catalase positive.
• No spores.
• Contain mycolic acids in cell wall.
• High lipid content @ 60% of dry weight of cells.

The above picture is an acid fast electron micrograph of M. tuberculosis

2. Taxonomic Description

Species are acid-fast during at least some stages of their growth. They are typically not nutritionally fastidious though growth of some species may be stimulated by serum or egg-yolk. Strict aerobes which use oxygen as terminal electron acceptor. Some species have strict temperature ranges for growth.M mariun and M. ulcerans grow at 32 C but not at 37 C. They are resistant to drying, alcohol, acid, alkali, many germicides, and most antibiotics. Virulence is associated with ability of pathogenic forms to survive after ingestion by macrophages and multiply intracellularly. There are approximately 84 species in current databases. These species are classified by being either Tuberculosis Mycobacterium (typical) or Nontuberculosis Mycobacterium (atypical, environmental organism or MOTTs [Mycobacterium Other Than Tuberculosis]).

The type species is M. tuberculosis. The above picture is an acid-fast stain of mycobacteria.

3. Isolation and Ecology

Members of the genus Mycobacterium are found as free-living saprophytes in soil and in water, or in some cases on plants. Some species have the ability to float on the surface of aqueous solutions. Some are parasites/pathogens of man and other animals. The two most notable human pathogens are M. tuberculosis and M. leprae. Many highly specific isolation and differential media are available for isolating mycobacteria.

MOTT species have been classified into 4 groups by Runyon. Group I organisms are photochromogens. Colonies grown in the dark are buff-colored but become yellow when exposed to light (M. kansaii). Group II organisms are known as scotochromogens and are pigmented when grown in the dark (M. scrofulaceum). Group III are nonphotochromogens. Colonies of this group do not change color on exposure to light. Finally, Group IV represents rapid growth Mycobacterium species. Typically organism of group IV grow in 6 days vs. the normal 12 day growth rate.

4. Additional Sources of Information

Briglia, M., R.L Eggen, W.M. deVos, and J.D. VanElsas. 1996. Rapid and sensitive method for detection of Mycobacterium chlorophenolicum PCP-1 in soil based on 16s rRNA gene targeted PCR. Appl. Environ. Microbiol. 62: 1478-1480

Ellner, P.D., and H.C. Neu. 1992 Understanding Infectious Disease. Mosby Year Book. St. Louis, Mo. 69-75

Iivanainen, K.K., P.J. Martikainen, M.L. Raisanen, and M.L. Katila. 1997. Mycobacteria in boreal coniferous forest soils. FEMS- Micobiology-Ecology 23:325-332

Johnsonifearlundu, Y.J. and J.B. Kaneene. 1997. Relationship between soil type and Mycobacterium paratuberculosis. Journal American Veterinary-Medical -Association. 210:1735-1740

5. Links to other Sites on Mycobacterium

General Information

http://microvet.arizona.edu/course/mic420

http://www.uct.ac.za/depts/mmi/lsteyn/lecture.html

M. tuberculosis

http://salk.utmem.edu/classes/micro/Mycobacterium.html
http://www.mds.qmw.ac.uk/medmicro/revision/modelanswer.html

MOTT

http://salk.utmem.edu/classes/micro/Mycobacterim.html