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'''Mycobacterium tuberculosis''' is the bacterium that causes most cases of tuberculosis. Sherris Medical Microbiology, Ryan KJ; Ray CG (editors), , , McGraw Hill, 2004, ISBN 0-8385-8529-9 It was first described on March 24, 1882 by Robert Koch, who subsequently received the Nobel Prize in physiology or medicine for this discovery in 1905; the bacterium is also known as ''Koch's bacillus''. The ''M. tuberculosis'' genome was sequenced in 1998.^[1][2]

Contents

Physiology

Identification

See Also

References

External links

Physiology

''M. tuberculosis'' is an obligate aerobe (Gram-positive mycobacterium). While mycobacteria do not seem to fit the Gram-positive category from an empirical standpoint (i.e. they do not retain the crystal violet stain), they are classified as an acid-fast Gram positive bacterium due to their lack of an outer cell membrane. ''M. tuberculosis'' divides every 15 to 20 hours—extremely slowly compared to other bacteria, which tend to have division times measured in minutes (for example, ''E. coli'' can divide roughly every 20 minutes). It is a small, rod-like bacillus that can withstand weak disinfectants and can survive in a dry state for weeks.

Identification

''M. tuberculosis'' is identified microscopically by its staining characteristics: it retains certain stains after being treated with acidic solution, and is thus classified as an "acid-fast bacillus" (AFB). In the most common staining technique, the Ziehl-Neelsen stain, AFB are stained a bright red, which stands out clearly against a blue background; therefore, the bacteria are sometimes called ''red snappers''.^[3] Acid-fast bacilli can also be visualized by fluorescent microscopy, and by auramine-rhodamine stain. The reason for the acid-fast staining is because of its thick waxy cell wall. Brock Biology of Microorganisms, Madigan, Michael; Martinko, John (editors), , , Prentice Hall, 2005, ISBN 0-13-144329-1 The waxy quality of the cell wall is mainly due to the presence of mycolic acids.
This waxy cell wall also is responsible for the typical caseous granuloma formation in tuberculosis. The component responsible, trehalose dimycolate, is called the cord factor. ''M. tuberculosis'' bacteria are difficult to grow. Lowenstein-Jensen media have traditionally been used for this purpose, but faster results can now be obtained using Middlebrook media.

See Also

★ Philip D'Arcy Hart

References

1. Deciphering the biology of ''Mycobacterium tuberculosis'' from the complete genome sequence., Cole ST; Brosch R; Parkhill J; ''et al''., , , Nature, 1998
2. Re-annotation of the genome sequence of ''Mycobacterium tuberculosis'' H37Rv, Camus JC; Pryor MJ; Medigue C; Cole ST., , , Microbiology, 148
3. Quarantining the noncompliant TB patient: catching the "Red Snapper", Flowers T, , , Journal of health and hospital law : a publication of the American Academy of Hospital Attorneys of the American Hospital Association, 1995

External links

★ Database of ''Mycobacterium tuberculosis'' genome sequences and related information.