acid-fast
American Heritage Dictionary:
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ac·id-fast
(ăs'ĭd-făst')
adj.
Not decolorized by acid after staining, as bacteria that retain dye after an acid rinse.
acid-fastness ac'id-fast'ness n.
adj.
Not decolorized by acid after staining, as bacteria that retain dye after an acid rinse.
acid-fastness ac'id-fast'ness n.
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adj.
Of or relating to bacteria that are not decolorized by an acidic alcohol solution after they have been stained.
ac'id-fast'ness n.Wikipedia on Answers.com:
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Acid-fast
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It has been suggested that Ziehl–Neelsen stain be merged into this article or section. (Discuss) Proposed since November 2011. |
Acid-fastness is a physical property of certain bacteria (and, less commonly, protozoa), specifically 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 stain - if you gram stained an acid-fast bacillus (AFB) the result would be an abnormal gram positive organism, which would indicate further testing), 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 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 acid fast bacilli 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).[3] Some bacteria may also be partially acid-fast. The eggs of Paragonimus westermani are actually destroyed by the stain, which can hinder diagnosis in patients who present with TB-like symptoms.
Notable acid-fast structures
Very few structures are acid fast; this makes staining for acid-fastness particularly useful in diagnosis. The following are notable examples of structures which are acid fast:
- All Mycobacteria - M. tuberculosis, M. leprae, M. smegmatis and atypical Mycobacterium
- Nocardia
- Head of sperm
- Bacterial spores, see Endospore
- Some coccidian parasites, such as Cryptosporidium parvum,[4] Isospora belli[5] and Cyclospora cayetanensis[6] cysts in faecal matter.
References
- ^ Madison B (2001). "Application of stains in clinical microbiology". Biotech Histochem 76 (3): 119–25. doi:10.1080/714028138. PMID 11475314.
- ^ a b Ryan KJ; Ray CG (editors) (2004). Sherris Medical Microbiology (4th ed.). McGraw Hill. ISBN 0-8385-8529-9.
- ^ Abe C (2003). "[Standardization of laboratory tests for tuberculosis and their proficiency testing]". Kekkaku 78 (8): 541–51. PMID 14509226.
- ^ Garcia LS, Bruckner DA, Brewer TC, Shimizu RY (July 1983). "Techniques for the recovery and identification of Cryptosporidium oocysts from stool specimens". J. Clin. Microbiol. 18 (1): 185–90. PMC 270765. PMID 6193138. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=270765.
- ^ Ng E, Markell EK, Fleming RL, Fried M (September 1984). "Demonstration of Isospora belli by acid-fast stain in a patient with acquired immune deficiency syndrome". J. Clin. Microbiol. 20 (3): 384–6. PMC 271334. PMID 6208216. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=271334.
- ^ Ortega YR, Sterling CR, Gilman RH, Cama VA, Díaz F (May 1993). "Cyclospora species--a new protozoan pathogen of humans". N. Engl. J. Med. 328 (18): 1308–12. doi:10.1056/NEJM199305063281804. PMID 8469253.
Online protocol examples
- Ziehl-Neelsen protocol (PDF format).
- Alternate Ellis & Zabrowarny method for staining AFB.
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The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.
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