Mycobacterium tuberculosis: Difference between revisions

Jump to navigation Jump to search
No edit summary
Line 9: Line 9:


==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>
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&mdash;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&mdash;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.
Line 40: Line 41:


<!--
<!--
==Overview==
The primary cause of tuberculosis is ''[[Mycobacterium tuberculosis]]'', an [[aerobic organism|aerobic]] [[bacterium]].


==Causes==
==Causes==


[[Image:Mycobacterium tuberculosis.jpg|300px|left|thumb|Scanning electron micrograph of ''[[Mycobacterium tuberculosis]]'']]


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>
Line 60: Line 57:
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>


===Morphology===
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.


===Physiology===


''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. ''M. tuberculosis'' divides every 15 to 20 hours&mdash;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.
===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% [[Potassium_hydroxide|KOH]] or [[Sodium_hydroxide|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''.<ref>{{cite journal |author=Flowers T |title=Quarantining the noncompliant TB patient: catching the "Red Snapper" |journal=Journal of health and hospital law : a publication of the American Academy of Hospital Attorneys of the American Hospital Association |volume=28 |issue=2 |pages=95-105 |year=1995 |pmid=10141473 |doi=}}</ref> The reason for the acid-fast staining is because of its thick waxy cell wall.<ref name=Brock>{{cite book | author = Madigan, Michael; Martinko, John (editors) | title = Brock Biology of Microorganisms | edition = 11th ed. | publisher = Prentice Hall | year = 2005 | id = ISBN 0-13-144329-1 }}</ref> The waxy quality of the cell wall is mainly due to the presence of [[Mycolic acid|mycolic acids]]. This waxy cell wall also is responsible for the typical [[Caseous necrosis|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.


-->
-->

Revision as of 14:30, 4 September 2014

Tuberculosis Microchapters

Home

Patient Information

Overview

Historical Perspective

Classification

Pathophysiology

Causes

Differentiating Tuberculosis from other Diseases

Epidemiology and Demographics

Risk Factors

Screening

Natural History, Complications and Prognosis

Children

HIV Coinfection

Diagnosis

History and Symptoms

Physical Examination

Laboratory Findings

Electrocardiogram

Chest X Ray

CT

MRI

Echocardiography or Ultrasound

Other Imaging Findings

Other Diagnostic Studies

Treatment

Medical Therapy

Special Conditions
Drug-resistant

Surgery

Primary Prevention

Secondary Prevention

Cost-Effectiveness of Therapy

Future or Investigational Therapies

Case Studies

Case #1

Mycobacterium tuberculosis On the Web

Most recent articles

Most cited articles

Review articles

CME Programs

Powerpoint slides

Images

American Roentgen Ray Society Images of Mycobacterium tuberculosis

All Images
X-rays
Echo & Ultrasound
CT Images
MRI

Ongoing Trials at Clinical Trials.gov

US National Guidelines Clearinghouse

NICE Guidance

FDA on Mycobacterium tuberculosis

CDC on Mycobacterium tuberculosis

Mycobacterium tuberculosis in the news

Blogs on Mycobacterium tuberculosis

Directions to Hospitals Treating Tuberculosis

Risk calculators and risk factors for Mycobacterium tuberculosis

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. 1.0 1.1 Ryan KJ; Ray CG (editors) (2004). Sherris Medical Microbiology (4th ed. ed.). McGraw Hill. ISBN 0-8385-8529-9.
  2. 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.
  3. Camus JC; Pryor MJ; Medigue C; Cole ST. (148). "Re-annotation of the genome sequence of Mycobacterium tuberculosis H37Rv". Microbiology. 2002: 2967&ndash, 2973.
  4. "Poliovirus".
  5. Lawn SD, Zumla AI (2011). "Tuberculosis". Lancet. 378 (9785): 57–72. doi:10.1016/S0140-6736(10)62173-3. PMID 21420161.
  6. 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.
  7. Madigan, Michael; Martinko, John (editors) (2005). Brock Biology of Microorganisms (11th ed. ed.). Prentice Hall. ISBN 0-13-144329-1.