Mycobacterium tuberculosis: Difference between revisions
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==Taxonomy== | ==Taxonomy== | ||
Cellular organisms; [[Bacteria]]; | 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> | ||
==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]] ( weakly [[Gram-positive]] [[mycobacterium]], hence Z.N. staining is used). 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.<ref name=Sherris /> ''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 [[disinfectant]]s and can survive in a dry state for weeks. | ''M. tuberculosis'' is an [[obligate aerobe]] ( weakly [[Gram-positive]] [[mycobacterium]], hence Z.N. staining is used). 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.<ref name=Sherris /> ''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 [[disinfectant]]s and can survive in a dry state for weeks. | ||
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==Causes== | ==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> | 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> | ||
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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> | 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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Revision as of 14:30, 4 September 2014
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Tuberculosis Microchapters |
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Mycobacterium tuberculosis On the Web |
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Soumya Sachdeva; João André Alves Silva, M.D. [2]
Overview
Mycobacterium tuberculosis is the bacterium that causes most cases of tuberculosis.[1] 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.[2][3]
Taxonomy
Cellular organisms; Bacteria; Actinobacteria; Actinobacteria; Actinobacteridae; Actinomycetales; Corynebacterineae; Mycobacteriaceae; Mycobacterium; Mycobacterium tuberculosis complex; M. tuberculosis[4]
Biology
Mycobacterium tuberculosis belongs to the Mycobacterium tuberculosis complex. This complex includes M. tuberculosis, M. bovis, M. africanum, M. canetti, and M. microti.[5]
M. tuberculosis is an obligate aerobe ( weakly Gram-positive mycobacterium, hence Z.N. staining is used). 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.[1] 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.
Structure
Slender, straight or slightly curved bacillus with rounded ends, occuring singly, in pairs or in small clumps. These bacilli are acid fast, non sporing, non capsulated and non motile.
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.
Diagnosis
Sputum is taken in 3 successive mornings as the number of organisms could be low, and the specimen is treated with 3% KOH or NaOH for liquefaction and decontamination. Gram stain should never be performed as the organism is an "acid-fast bacillus" (AFB), meaning that it retains certain stains after being treated with acidic solution. 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.[6] The reason for the acid-fast staining is because of its thick waxy cell wall.[7] 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. A grading system exists for interpretation of the microscopic findings based on the number of organisms obsereved in each field. Acid-fast bacilli can also be visualized by fluorescent microscopy using auramine-rhodamine stain which makes them appear somewhat golden in color. Also, M. tuberculosis is grown on a selective medium known as Lowenstein-Jensen medium which have traditionally been used for this purpose. However, this method is quite slow; as this organism requires 6-8 months to grow which certainly delays reporting of results. A faster results can now be obtained using Middlebrook medium.
References
- ↑ 1.0 1.1 Ryan KJ; Ray CG (editors) (2004). Sherris Medical Microbiology (4th ed. ed.). McGraw Hill. ISBN 0-8385-8529-9.
- ↑ Cole ST; Brosch R; Parkhill J; et al. (1998). "Deciphering the biology of Mycobacterium tuberculosis from the complete genome sequence". Nature. 393: 537&ndash, 544.
- ↑ Camus JC; Pryor MJ; Medigue C; Cole ST. (148). "Re-annotation of the genome sequence of Mycobacterium tuberculosis H37Rv". Microbiology. 2002: 2967&ndash, 2973.
- ↑ "Poliovirus".
- ↑ Lawn SD, Zumla AI (2011). "Tuberculosis". Lancet. 378 (9785): 57–72. doi:10.1016/S0140-6736(10)62173-3. PMID 21420161.
- ↑ Flowers T (1995). "Quarantining the noncompliant TB patient: catching the "Red Snapper"". Journal of health and hospital law : a publication of the American Academy of Hospital Attorneys of the American Hospital Association. 28 (2): 95–105. PMID 10141473.
- ↑ Madigan, Michael; Martinko, John (editors) (2005). Brock Biology of Microorganisms (11th ed. ed.). Prentice Hall. ISBN 0-13-144329-1.