Acid-fast


Acid-fast

Acid-fastness is a physical property of some bacteria referring to their resistance to decolorization by acids during staining procedures.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 |doi=10.1080/714028138] 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 ]

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".

The high mycolic acid content of certain bacterial cell walls, like those of "Mycobacteria", 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. Another method is the Kinyoun method, in which the bacteria are stained bright red and stand out clearly against a green background. Acid-fast bacteria can also be visualized by fluorescence microscopy using specific fluorescent dyes (auramine-rhodamine stain, for example).cite journal |author=Abe C |title= [Standardization of laboratory tests for tuberculosis and their proficiency testing] |journal=Kekkaku |volume=78 |issue=8 |pages=541–51 |year=2003 |pmid=14509226] Some bacteria may also be partially acid-fast.

Notable Acid fast structures

Very few structures are acid fast, this makes staining for acid-fastness particularly useful in diagnosis.

* All Mycobacteria - "M.tuberculosis", "M.Leprae", "M.smegmatis" and atypical "Mycobacterium"
* "Nocardia"
* Head of sperm
* Bacterial spores
* "Cryptosporidium parvum", "Isospora" and "Cyclospora" cysts

References

Online protocol examples

* [http://www-medlib.med.utah.edu/WebPath/HISTHTML/MANUALS/AFB.PDF Ziehl-Neelsen] protocol (PDF format).
* Alternate [http://www.nottingham.ac.uk/pathology/protocols/afb.html Ellis & Zabrowarny method] for staining AFB.


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Look at other dictionaries:

  • acid-fast — [as′id fast΄] adj. that does not readily lose its color when exposed to acids after being stained: said esp. of certain bacteria and tissues …   English World dictionary

  • acid-fast — Denoting bacteria that are not decolorized by acid alcohol after having been stained with dyes such as basic fuchsin; e.g., the mycobacteria and nocardiae. * * * acid fast as əd .fast adj not easily decolorized by acids (as when stained) used esp …   Medical dictionary

  • acid-fast — adj. 1) describing bacteria that have been stained and continue to hold the stain after treatment with an acidic solution. For example, tuberculosis bacteria are acid fast when stained with a carbol fuchsin preparation. 2) describing a stain that …   The new mediacal dictionary

  • acid-fast — acid fastness, n. /as id fast , fahst /, adj. resistant to decolorizing by acidified alcohol after staining. [1900 05] * * * …   Universalium

  • acid-fast — adjective not easily decolorized by acid solutions; pertains to micro organisms (especially the tubercle bacillus that causes tuberculosis) • Similar to: ↑impervious, ↑imperviable * * * ˈ ̷ ̷ ̷ ̷ˌ ̷ ̷ adjective : not easily decolorized by acids… …   Useful english dictionary

  • acid-fast — /ˈæsəd fast/ (say asuhd fahst) adjective resistant to decolourisation by acid after staining …   Australian English dictionary

  • acid-fast — ac′id fast adj. lab resistant to decolorizing by acidified alcohol after staining • Etymology: 1900–05 ac′id fast ness, n …   From formal English to slang

  • acid fast — Refers to bacteria like the mycobacteria that cannot be easily decolorized with acid alcohol after being stained with dyes such as basic fuchsin …   Dictionary of microbiology

  • acid-fast — adjective Date: 1903 not easily decolorized by acids …   New Collegiate Dictionary

  • acid-fast — adjective (histology) of bacteria that retain their stain when treated with an acidic solution …   Wiktionary


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