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{{Tuberculosis}}
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{{SK}} M. Tuberculosis


==Overview==
==Overview==
 
[[Mycobacterium tuberculosis]] is the [[bacterium]] responsible for [[tuberculosis]]. M. tuberculosis is an [[obligate aerobe]], [[capsule|non-encapsulated]], [[motility|non-motile]], [[acid-fast]] [[bacillus]]. .  M. tuberculosis is one of the '''Mycobacterium tuberculosis''' complex, which also includes [[bacteria]], such as [[Mycobacterium bovis|M. bovis]] and M. africanum. The bacterium has a very slow rate of [[replication]], and its [[genetic]] variations account for the different [[strains]] and the growing [[drug resistance]].  M. tuberculosis has [[tropism]] for different kinds of human cells, with preference for cells of the [[lung]]. The main [[natural reservoir]] for ''M. [[tuberculosis]] are'' [[Human]] beings'';'' however, the [[bacteria]] can also [[Infection|infect]] other [[species]].
'''''Mycobacterium tuberculosis''''' is the [[bacterium]] that causes most cases of [[tuberculosis]].<ref name=Sherris>{{cite book | author = Ryan KJ; Ray CG (editors) | title = Sherris Medical Microbiology | edition = 4th ed. | publisher = McGraw Hill | year = 2004 | id = ISBN 0-8385-8529-9 }}</ref>  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.<ref>{{cite journal | author = Cole ST; Brosch R; Parkhill J; ''et al''. | title = Deciphering the biology of ''Mycobacterium tuberculosis'' from the complete genome sequence. | journal = Nature | year = 1998 | volume = 393 | pages = 537&ndash;544 | url= http://www.nature.com/nature/journal/v393/n6685/full/393537a0_fs.html}}</ref><ref>{{cite journal
| author = Camus JC; Pryor MJ; Medigue C; Cole ST. | title = Re-annotation of the genome sequence of ''Mycobacterium tuberculosis'' H37Rv | journal = Microbiology | year = 148 | volume = 2002 | pages = 2967&ndash;2973 | url= http://mic.sgmjournals.org/cgi/content/full/148/10/2967?view=full&pmid=12368430}}</ref>


==Taxonomy==
==Taxonomy==
Cellular organisms; [[Bacteria]]; [[Actinobacteria]]; [[Actinobacteria]]; [[Actinobacteridae]]; [[Actinomycetales]]; [[Corynebacterineae]]; [[Mycobacteriaceae]]; ''[[Mycobacterium]]'';  Mycobacterium tuberculosis complex; ''M. tuberculosis''<ref name=NCBI>{{cite web | title = Poliovirus | url = http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=1773 }}</ref>
{| style="float: right;"
|[[File:M.tuberculosis1.jpg|200px|thumb|none|Computer-generated image of a cluster of rod-shaped drug-resistant Mycobacterium tuberculosis bacteria.<SMALL> ''Image provided by the CDC [http://phil.cdc.gov/phil/details.asp Centers for Disease Control and Prevention] ''<ref>{{Cite web | title = http://phil.cdc.gov/phil/details.asp | url = http://phil.cdc.gov/phil/details.asp}}</ref></SMALL>]]
|-
|[[File:M. tuberculosis2.jpg|200px|thumb|none|Thin agar culture plates reveal the results of a drug susceptibility test on Mycobacterium tuberculosis bacteria <SMALL> ''Image provided by the CDC [http://phil.cdc.gov/phil/details.asp Centers for Disease Control and Prevention] ''<ref>{{Cite web | title = http://phil.cdc.gov/phil/details.asp | url = http://phil.cdc.gov/phil/details.asp}}</ref></SMALL>]]
|}
Cellular organisms; [[bacteria]]; [[Actinobacteria]]; [[Actinobacteria]]; [[Actinobacteridae]]; [[Actinomycetales]]; [[Corynebacterineae]]; [[Mycobacteriaceae]]; ''[[Mycobacterium]]'';  Mycobacterium tuberculosis complex; ''M. tuberculosis''<ref name="NCBI">{{cite web | title = Mycobacterium tuberculosis | url = http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=1773 }}</ref>


==Biology==
==Biology==
''Mycobacterium tuberculosis'' belongs to the Mycobacterium tuberculosis complex.  This complex includes ''M. tuberculosis'', ''M. bovis'', ''M. africanum'', ''M. canetti'', and ''M. microti''.<ref name="pmid21420161">{{cite journal| author=Lawn SD, Zumla AI| title=Tuberculosis. | journal=Lancet | year= 2011 | volume= 378 | issue= 9785 | pages= 57-72 | pmid=21420161 | doi=10.1016/S0140-6736(10)62173-3 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=21420161  }} </ref>


''M. tuberculosis'' is an [[obligate aerobe]], [[capsule|non-encapsulated]], [[motility|non-motile]], [[acid-fast]] [[bacillus]]. Slender, straight or slightly curved [[bacillus]] with rounded ends, occuring singly, in pairs or in small clumps. It does not form [[spores]] and its ideal growing environment includes tissues with high levels of oxygen. It cannot be considered gram positive or gram negative due to its high lipid cell wall, that is impermeable to the dyes until combined with an alcohol. On microscopic examination of [[sputum]] samples, the bacteria cannot be distinguished from other [[acid-fast]] bacteria, such as [[Nocardia]] app.<ref name="pmid21420161">{{cite journal| author=Lawn SD, Zumla AI| title=Tuberculosis. | journal=Lancet | year= 2011 | volume= 378 | issue= 9785 | pages= 57-72 | pmid=21420161 | doi=10.1016/S0140-6736(10)62173-3 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=21420161  }} </ref>
* ''[[Mycobacterium tuberculosis]]'' belongs to the Mycobacterium tuberculosis complex.  This complex includes ''M. tuberculosis'', ''[[Mycobacterium bovis|M. bovis]]'', ''[[M. africanum]]'', ''M. canetti'', and [[M. microti.|''M. microti''.]]<ref name="pmid21420161">{{cite journal| author=Lawn SD, Zumla AI| title=Tuberculosis. | journal=Lancet | year= 2011 | volume= 378 | issue= 9785 | pages= 57-72 | pmid=21420161 | doi=10.1016/S0140-6736(10)62173-3 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=21420161  }} </ref>


''M. tuberculosis'' has a very slow rate of replication, taking about 15 to 20 hours to divide. This characteristic, added to its ability to remain in latent state for long periods of time, account for the treatment duration required for infected patients.<ref name="pmid21420161">{{cite journal| author=Lawn SD, Zumla AI| title=Tuberculosis. | journal=Lancet | year= 2011 | volume= 378 | issue= 9785 | pages= 57-72 | pmid=21420161 | doi=10.1016/S0140-6736(10)62173-3 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=21420161  }} </ref>
* ''M. tuberculosis'' is an [[obligate aerobe]], [[capsule|non-encapsulated]], [[motility|non-motile]], [[acid-fast]] [[bacillus]].
* Its shape is [[slender]], straight or slightly [[curved]] [[bacillus]] with rounded ends.
* It can be present [[singly]], in pairs or in small groups or [[clumps]].
* It cannot form [[spores]].
* It favors [[Tissue (biology)|tissues]] with high [[oxygen]] levels. 
* Due to the high [[lipid]] and [[mycolic acid]] content of its [[cell wall]], It stains weakly [[gram-positive]] or does not retain the [[dye]]. 
* [[Microscopic examination]] of [[sputum]] [[samples]] cannot differentiate it  from other [[acid-fast]] bacteria, such as [[Nocardia]] spp.<ref name="pmid21420161">{{cite journal| author=Lawn SD, Zumla AI| title=Tuberculosis. | journal=Lancet | year= 2011 | volume= 378 | issue= 9785 | pages= 57-72 | pmid=21420161 | doi=10.1016/S0140-6736(10)62173-3 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=21420161  }} </ref> 
* ''M. [[tuberculosis]]'' [[divides]] every 15-20 hours which is considered an extremely low rate of [[Division (biology)|division]]. This feature, in addition to its ability to remain latent for long time, are responsible for the long [[treatment]] duration needed.<ref name="pmid21420161">{{cite journal| author=Lawn SD, Zumla AI| title=Tuberculosis. | journal=Lancet | year= 2011 | volume= 378 | issue= 9785 | pages= 57-72 | pmid=21420161 | doi=10.1016/S0140-6736(10)62173-3 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=21420161  }} </ref>
* It can withstand dryness for weeks and also weak [[Disinfectant|disinfectants]].


Genetic variances in the genome of ''M. tuberculosis'' lead to important phenotypical changes. There are many different [[strains]] of the bacteria, however, 6 of them were noted to be associated with specific geographic areas. This data is important since 3 [[strains]], the Beijing family, strain W and the W-like strains, were noted to be associated with resistance to treatment drugs.<ref name="pmid19483712">{{cite journal| author=Smith NH, Hewinson RG, Kremer K, Brosch R, Gordon SV| title=Myths and misconceptions: the origin and evolution of Mycobacterium tuberculosis. | journal=Nat Rev Microbiol | year= 2009 | volume= 7 | issue= 7 | pages= 537-44 | pmid=19483712 | doi=10.1038/nrmicro2165 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=19483712  }} </ref><ref name="pmid17448936">{{cite journal| author=Gagneux S, Small PM| title=Global phylogeography of Mycobacterium tuberculosis and implications for tuberculosis product development. | journal=Lancet Infect Dis | year= 2007 | volume= 7 | issue= 5 | pages= 328-37 | pmid=17448936 | doi=10.1016/S1473-3099(07)70108-1 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=17448936  }} </ref>
* Genetic variations in the ''M. tuberculosis'' [[genome]] lead to important [[phenotypical]] changes. As a result, there are several variable [[strains]] of the [[bacteria]], six of which have particular [[Geographical isolation|geographical]] distribution. Three [[strains]], the ''[[Beijing family]]'', ''strain W'' and the ''W-like strains'', were reported to be associated with higher [[Incidence (epidemiology)|incidence]] of [[multi-drug resistance]].<ref name="pmid19483712">{{cite journal| author=Smith NH, Hewinson RG, Kremer K, Brosch R, Gordon SV| title=Myths and misconceptions: the origin and evolution of Mycobacterium tuberculosis. | journal=Nat Rev Microbiol | year= 2009 | volume= 7 | issue= 7 | pages= 537-44 | pmid=19483712 | doi=10.1038/nrmicro2165 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=19483712  }} </ref><ref name="pmid17448936">{{cite journal| author=Gagneux S, Small PM| title=Global phylogeography of Mycobacterium tuberculosis and implications for tuberculosis product development. | journal=Lancet Infect Dis | year= 2007 | volume= 7 | issue= 5 | pages= 328-37 | pmid=17448936 | doi=10.1016/S1473-3099(07)70108-1 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=17448936  }} </ref>


==Tropism==
==Tropism==
There is no particular tissue [[tropism]] for M. [[tuberculosis]] and it can infect almost all human tissues. However, M. [[tuberculosis]] prefers tissues with high levels of [[oxygen]] , hence, [[pulmonary tuberculosis]] has the highest rate. <ref name="pmid21420161">{{cite journal| author=Lawn SD, Zumla AI| title=Tuberculosis. | journal=Lancet | year= 2011 | volume= 378 | issue= 9785 | pages= 57-72 | pmid=21420161 | doi=10.1016/S0140-6736(10)62173-3 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=21420161  }} </ref>


==Natural Reservoir==
==Natural Reservoir==
Human beings are the main [[natural reservoir]] for ''M. tuberculosis'', however, the bacteria may infect other [[species]].<ref name="pmid21420161">{{cite journal| author=Lawn SD, Zumla AI| title=Tuberculosis. | journal=Lancet | year= 2011 | volume= 378 | issue= 9785 | pages= 57-72 | pmid=21420161 | doi=10.1016/S0140-6736(10)62173-3 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=21420161  }} </ref>
The main [[natural reservoir]] for ''M. [[tuberculosis]] are [[Human]] beings;'' however, the [[bacteria]] can also [[Infection|infect]] other [[species]].<ref name="pmid21420161">{{cite journal| author=Lawn SD, Zumla AI| title=Tuberculosis. | journal=Lancet | year= 2011 | volume= 378 | issue= 9785 | pages= 57-72 | pmid=21420161 | doi=10.1016/S0140-6736(10)62173-3 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=21420161  }} </ref>
 
==Resistance==
 
Mycobacteria are killed at 60 degree celsius in 15-20 minutes.
They are sensitive to UV rays and sunlight.
They are relatively resistant to 5% phenol, 15% sulphuric acid, 5% oxalic acid, 4% sodium hydroxide.
The bacillus are destroyed by tincture of sodium in five minutes and by 80% ethanol in 2-10 minutes.


==References==
==References==
{{reflist|2}}
{{reflist|2}}
[[Category:Acid fast bacilli]]
[[Category:Acid fast bacilli]]
[[Category:Actinobacteria]]
[[Category:Actinobacteria]]
[[Category:Gram positive bacteria]]
[[Category:Gram positive bacteria]]
[[Category:Infectious disease]]
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==Causes==
The primary cause of TB, ''[[Mycobacterium tuberculosis]]'' (M. TB), is an [[aerobic organism|aerobic]] [[bacterium]] that [[cell division|divides]] every 16 to 20 hours, an extremely slow rate compared with other bacteria, which usually divide in less than an hour.<ref name=Cox_2004>{{cite journal |author=Cox R |title=Quantitative relationships for specific growth rates and macromolecular compositions of ''Mycobacterium tuberculosis'', ''Streptomyces coelicolor'' A3(2) and ''Escherichia coli'' B/r: an integrative theoretical approach |journal=Microbiology |volume=150 |issue=Pt 5 |pages=1413–26 |year=2004 |url=http://mic.sgmjournals.org/cgi/content/full/150/5/1413?view=long&pmid=15133103#R35 | pmid = 15133103}}</ref> (For example, one of the fastest-growing bacteria is a strain of ''[[E. coli]]'' that can divide roughly every 20 minutes.) Since MTB has a cell wall but lacks a [[phospholipid]] [[Bacterial cell structure|outer membrane]], it is [[Tuberculosis classification|classified]] as a [[Gram-positive]] bacterium. However, if a [[Gram stain]] is performed, MTB either stains very weakly Gram-positive or does not retain dye due to the high lipid & [[mycolic acid]] content of its cell wall.<ref name=Madison_2001>{{cite journal |author=Madison B |title=Application of stains in clinical microbiology. |journal=Biotech Histochem |volume=76 |issue=3 |pages=119-25 |year=2001 |pmid=11475314}}</ref> MTB is a small rod-like [[bacillus]] that can withstand weak [[disinfectant]]s and survive in a [[Endospore|dry state]] for weeks. In nature, the bacterium can grow only within the cells of a [[host (biology)|host]] organism, but ''M. tuberculosis'' can be cultured ''[[in vitro]]''.<ref name=Parish_1999>{{cite journal |author=Parish T, Stoker N |title=Mycobacteria: bugs and bugbears (two steps forward and one step back) |journal=Mol Biotechnol |volume=13 |issue=3 |pages=191–200 |year=1999 | pmid = 10934532}}</ref>
Using certain [[histology|histological]] techniques on expectorate samples from [[phlegm]] (also called sputum), scientists can identify MTB under a regular microscope. Since MTB retains certain stains after being treated with acidic solution, it is classified as an [[acid-fast bacillus]] (AFB).<ref name=Madison_2001>{{cite journal |author=Madison B |title=Application of stains in clinical microbiology |journal=Biotech Histochem |volume=76 |issue=3 |pages=119-25 |year=2001 | pmid = 11475314}}</ref> The most common staining technique, the [[Ziehl-Neelsen stain]], dyes AFBs a bright red that stands out clearly against a blue background. Other ways to visualize AFBs include an [[auramine-rhodamine stain]] and [[Fluorescence microscope|fluorescent microscopy]].
The ''M. tuberculosis'' complex includes 3 other TB - causing [[mycobacterium|mycobacteria]]: ''[[Mycobacterium bovis|M. bovis]]'', ''[[Mycobacterium africanum|M. africanum]]'' and ''[[Mycobacterium microti|M. microti]]''. The first two only very rarely cause disease in [[immunocompetent]] people. On the other hand, although ''M. microti'' is not usually [[pathogen]]ic, it is possible that the [[prevalence]] of ''M. microti'' infections has been underestimated.<ref name=Niemann_2000>{{cite journal |author=Niemann S, Richter E, Dalügge-Tamm H, Schlesinger H, Graupner D, Königstein B, Gurath G, Greinert U, Rüsch-Gerdes S |title=Two cases of ''Mycobacterium microti'' derived tuberculosis in HIV-negative immunocompetent patients |journal=Emerg Infect Dis |volume=6 |issue=5 |pages=539-42 |year=2000 |pmid = 10998387}}</ref>
Other known pathogenic [[Mycobacterium|mycobacteria]] include ''[[Mycobacterium leprae]]'', [[Mycobacterium avium complex|''Mycobacterium avium'']] and ''M. kansasii''. The last two are part of the [[nontuberculous mycobacteria]] (NTM) group. Nontuberculous mycobacteria cause neither TB nor [[leprosy]], but they do cause pulmonary diseases resembling TB.<ref name=ALA_1997>{{cite journal |author= |title=Diagnosis and treatment of disease caused by nontuberculous mycobacteria. This official statement of the American Thoracic Society was approved by the Board of Directors, March 1997. Medical Section of the American Lung Association |journal=Am J Respir Crit Care Med |volume=156 |issue=2 Pt 2 |pages=S1–25 |year=1997 |pmid = 9279284}}</ref>
===Evolution===
During its evolution, ''M. tuberculosis'' has lost numerous [[Coding region|coding]] and non-coding regions in its [[genome]], losses that can be used to distinguish between strains of the bacteria. The implication is that ''M. tuberculosis'' strains differ geographically, so their genetic differences can be used to track the origins and movement of each strain.<ref name=Rao_2005>{{cite journal |author=Rao K, Kauser F, Srinivas S, Zanetti S, Sechi L, Ahmed N, Hasnain S |title=Analysis of genomic downsizing on the basis of region-of-difference polymorphism profiling of Mycobacterium tuberculosis patient isolates reveals geographic partitioning |journal=J Clin Microbiol |volume=43 |issue=12 |pages=5978–82 |year=2005 | pmid = 16333085}}</ref>
-->

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Mashal Awais, M.D.[2]; João André Alves Silva, M.D. [3]

This page is about microbiologic aspects of the organism(s).  For clinical aspects of the disease, see Tuberculosis.

Synonyms and keywords: M. Tuberculosis

Overview

Mycobacterium tuberculosis is the bacterium responsible for tuberculosis. M. tuberculosis is an obligate aerobe, non-encapsulated, non-motile, acid-fast bacillus. . M. tuberculosis is one of the Mycobacterium tuberculosis complex, which also includes bacteria, such as M. bovis and M. africanum. The bacterium has a very slow rate of replication, and its genetic variations account for the different strains and the growing drug resistance. M. tuberculosis has tropism for different kinds of human cells, with preference for cells of the lung. The main natural reservoir for M. tuberculosis are Human beings; however, the bacteria can also infect other species.

Taxonomy

Computer-generated image of a cluster of rod-shaped drug-resistant Mycobacterium tuberculosis bacteria. Image provided by the CDC Centers for Disease Control and Prevention [1]
Thin agar culture plates reveal the results of a drug susceptibility test on Mycobacterium tuberculosis bacteria Image provided by the CDC Centers for Disease Control and Prevention [2]

Cellular organisms; bacteria; Actinobacteria; Actinobacteria; Actinobacteridae; Actinomycetales; Corynebacterineae; Mycobacteriaceae; Mycobacterium; Mycobacterium tuberculosis complex; M. tuberculosis[3]

Biology

Tropism

There is no particular tissue tropism for M. tuberculosis and it can infect almost all human tissues. However, M. tuberculosis prefers tissues with high levels of oxygen , hence, pulmonary tuberculosis has the highest rate. [4]

Natural Reservoir

The main natural reservoir for M. tuberculosis are Human beings; however, the bacteria can also infect other species.[4]

References

  1. ↑ "http://phil.cdc.gov/phil/details.asp". External link in |title= (help)
  2. ↑ "http://phil.cdc.gov/phil/details.asp". External link in |title= (help)
  3. ↑ "Mycobacterium tuberculosis".
  4. ↑ 4.0 4.1 4.2 4.3 4.4 Lawn SD, Zumla AI (2011). "Tuberculosis". Lancet. 378 (9785): 57–72. doi:10.1016/S0140-6736(10)62173-3. PMID 21420161.
  5. ↑ Smith NH, Hewinson RG, Kremer K, Brosch R, Gordon SV (2009). "Myths and misconceptions: the origin and evolution of Mycobacterium tuberculosis". Nat Rev Microbiol. 7 (7): 537–44. doi:10.1038/nrmicro2165. PMID 19483712.
  6. ↑ Gagneux S, Small PM (2007). "Global phylogeography of Mycobacterium tuberculosis and implications for tuberculosis product development". Lancet Infect Dis. 7 (5): 328–37. doi:10.1016/S1473-3099(07)70108-1. PMID 17448936.
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