acid-fast bacillus

Acid-fastness is a physical property of some bacteria referring to their resistance to decolorization by acids during staining procedures.[1][2]

Acid-fast organisms are difficult to characterize using standard microbiological techniques (e.g. Gram staining), though they can be stained using concentrated dyes, particularly when the staining process is combined with heat. Once stained, these organisms resist the dilute acid and/or ethanol-based de-colorization procedures common in many staining protocols—hence the name acid-fast.[2]

The high mycolic acid content of certain bacterial cell walls, like those of Mycobacterium, is responsible for the staining pattern of poor absorption followed by high retention. The most common staining technique used to identify acid-fast bacteria is the Ziehl-Neelsen stain, in which the bacteria are stained bright red and stand out clearly against a blue background. Acid-fast bacteria can also be visualized by fluorescence microscopy using specific fluorescent dyes (auramine-rhodamine stain, for example).[3] Some bacteria may also be partially acid-fast.

Only a few types of bacteria are acid-fast, notably members of the Mycobacterium. Most are rod-shaped, termed acid-fast bacilli (AFB), but other forms also occur. Medically the most important AFB is Mycobacterium tuberculosis. Genera like Nocardia and Corynebacterium are also notable examples.

References

1. ^ Madison B (2001). "Application of stains in clinical microbiology". Biotech Histochem 76 (3): 119-25. PMID 11475314. 
2. ^ Ryan KJ; Ray CG (editors) (2004). Sherris Medical Microbiology, 4th ed., McGraw Hill. ISBN 0-8385-8529-9. 
3. ^ Abe C (2003). "[Standardization of laboratory tests for tuberculosis and their proficiency testing]". Kekkaku 78 (8): 541-51. PMID 14509226. 

Online protocol examples

Bacteria

Phyla

Actinobacteria
Aquificae
Chlamydiae
Bacteroidetes/Chlorobi
Chloroflexi
Chrysiogenetes
Cyanobacteria
Deferribacteres
Deinococcus-Thermus
Dictyoglomi
Fibrobacteres/Acidobacteria
Firmicutes
Fusobacteria
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Staining is a biochemical technique of adding a class-specific (DNA, proteins, lipids, carbohydrates) dye to a substrate to qualify or quantify the presence of a specific compound. It is similar to fluorescent tagging.
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Gram staining (or Gram's method) is an empirical method of differentiating bacterial species into two large groups (Gram-positive and Gram-negative) based on the chemical and physical properties of their cell walls.
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Mycolic acids are long fatty acids found in the cell walls of the mycolata taxon, a group of bacteria which includes Mycobacterium tuberculosis, the causative agent of the disease tuberculosis. They form the major component of the cell wall of mycolata species.
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cell wall is a fairly rigid layer surrounding a cell, located external to the cell membrane, which provides the cell with structural support, protection, and acts as a filtering mechanism. The cell wall also prevents over-expansion when water enters the cell.
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Mycobacteriaceae

Genus: Mycobacterium
Lehmann & Neumann 1896

Species

See below.

Mycobacterium is a genus of Actinobacteria, given its own family, the Mycobacteriaceae.
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Ziehl-Neelsen stain, also known as the acid-fast stain, was first described by two German doctors; Franz Ziehl (1859 to 1926), a bacteriologist and Friedrich Neelsen (1854 to 1894), a pathologist. It is a special bacteriological stain used to identify acid-fast Mycobacteria.
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auramine-rhodamine stain (AR), also known as the Truant auramine-rhodamine stain, is a histological technique used to visualizee acid-fast bacilli using fluorescence microscopy, notably species in the Mycobacterium genus.
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Mycobacteriaceae

Genus: Mycobacterium
Lehmann & Neumann 1896

Species

See below.

Mycobacterium is a genus of Actinobacteria, given its own family, the Mycobacteriaceae.
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M. tuberculosis

Binomial name
Mycobacterium tuberculosis
Zopf 1883

Mycobacterium tuberculosis is the bacterium that causes most cases of tuberculosis.
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Nocardia
Trevisan 1889

Nocardia is a genus of Gram-positive, catalase-positive, rod-shaped bacteria; some species are pathogenic (nocardiosis).[1] Nocardia are found worldwide in soil that is rich with organic matter.
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Corynebacteriaceae

Genus: Corynebacterium
Lehmann & Neumann 1896

Species

See text.
Corynebacterium is a genus of Gram-positive, facultatively anaerobic, non-motile, rod-shaped actinobacteria.
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Portable Document Format (PDF)

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