Tuberculosis causes: Difference between revisions
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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]]. | 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> | 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> | 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> | ||
Revision as of 15:02, 27 December 2012
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
The primary cause of tuberculosis is Mycobacterium tuberculosis, an aerobic bacterium.
Causes
The primary cause of TB , Mycobacterium tuberculosis (M. TB), is an aerobic bacterium that divides every 16 to 20 hours, an extremely slow rate compared with other bacteria, which usually divide in less than an hour.[1] (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 outer membrane, it is 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.[2] MTB is a small rod-like bacillus that can withstand weak disinfectants and survive in a dry state for weeks. In nature, the bacterium can grow only within the cells of a host organism, but M. tuberculosis can be cultured in vitro.[3]
Using certain 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).[2] 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 fluorescent microscopy.
The M. tuberculosis complex includes 3 other TB - causing mycobacteria: M. bovis, M. africanum and M. microti. The first two only very rarely cause disease in immunocompetent people. On the other hand, although M. microti is not usually pathogenic, it is possible that the prevalence of M. microti infections has been underestimated.[4]
Other known pathogenic mycobacteria include Mycobacterium leprae, 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.[5]
Evolution
During its evolution, M. tuberculosis has lost numerous 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.[6]
References
- ↑ Cox R (2004). "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". Microbiology. 150 (Pt 5): 1413–26. PMID 15133103.
- ↑ 2.0 2.1 Madison B (2001). "Application of stains in clinical microbiology". Biotech Histochem. 76 (3): 119–25. PMID 11475314.
- ↑ Parish T, Stoker N (1999). "Mycobacteria: bugs and bugbears (two steps forward and one step back)". Mol Biotechnol. 13 (3): 191–200. PMID 10934532.
- ↑ Niemann S, Richter E, Dalügge-Tamm H, Schlesinger H, Graupner D, Königstein B, Gurath G, Greinert U, Rüsch-Gerdes S (2000). "Two cases of Mycobacterium microti derived tuberculosis in HIV-negative immunocompetent patients". Emerg Infect Dis. 6 (5): 539–42. PMID 10998387.
- ↑ "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". Am J Respir Crit Care Med. 156 (2 Pt 2): S1–25. 1997. PMID 9279284.
- ↑ Rao K, Kauser F, Srinivas S, Zanetti S, Sechi L, Ahmed N, Hasnain S (2005). "Analysis of genomic downsizing on the basis of region-of-difference polymorphism profiling of Mycobacterium tuberculosis patient isolates reveals geographic partitioning". J Clin Microbiol. 43 (12): 5978–82. PMID 16333085.