Nowaday,when we hear of acid fast organism,we primarily think of Mycobacterium species such as tuberculosis,leprae etc. Acid-fast organisms such as members of the genus Mycobacterium are differentiated and identify using an acid fast stain such as Ziehl Neelsen stain
Acid-fastness refers to a physical property of certain bacterial or group of bacteria and eukaryotic cells, as well as some sub-cellular structures found in a organism, which makes it resistant to decolorization by the acid alcohol during laboratory staining procedures.
Acid-fast organisms are characterized by wax-like, nearly impermeable cell walls; they also contain mycolic acid and large amounts of fatty acids, waxes, and complex lipids and are highly resistant to disinfectants and dry conditions.
Once these structures or organisms are stained as part of a sample e.g sputum,urine,sperm,stools, it can resist the acid and/or ethanol-based decolorization solution hence the name acid-fast
Principles involve stain acid fast organisms
Because the cell wall is so resistant to most compounds, acid-fast organisms require a special staining technique here we use the Ziehl neelsen stain technique
- The primary stain used in acid-fast staining, carbolfuchsin, is lipid-soluble and contains phenol, which helps the stain penetrate the cell wall.
- This is further assisted by the addition of heat.
- The smear is then rinsed with a very strong decolorizer, which strips the stain from all non-acid-fast cells but does not permeate the cell wall of acid-fast organisms so they stains pink .
- The decolorized non-acid-fast cells then take up the counterstain (Gentian violet staining purple).
Note that the mechanisms of acid-fastness will vary by species or structures, although the most well-known example exist among the genus Mycobacterium, particularly the species responsible for causing tuberculosis and leprosy.
These Mycobacteria species acid fastness is due to the high their mycolic acid, a lipid in their walls which is responsible for the staining pattern of poor absorption followed by high retention Although difficult to stain, once the stain goes into the cell wall, the cell wall becomes resistant to acid alcohol decolorization.
The Following are list of acid fast organism and cellular structures
- Head of sperm cells
- Spore of bacteria mostly endospores
- Legionella micdadei
- Some cellular inclusions like
- The Cytoplasmic inclusion bodies seen in neurons in layer 5 of cerebral cortex neuronal ceroid lipofuscinosis (Batten disease).
- The Nuclear inclusion bodies seen in situation such as Lead poisoning and Bismuth poisoning.
- In stools sample, Oocysts of some coccidian parasites such as Cryptosporidium parvum, Isospora belli,microsporidium and Cyclospora cayetanensis.
- A few other helminth and protozoa parasites such as Sarcocystis
- Taenia saginata eggs which stain well but not Taenia solium eggs (though they can’t be distinguish)
- Hydatid cysts, especially their “hooklets” stain irregularly with
Ziehl-Neelsen stain but emanate bright red fluorescence under green light, and can aid detection in moderately heavy backgrounds or with scarce hooklets.
- Schistosoma mansoni egg shells are
Ziehl-Neelsen staining positive
- Some fungal yeast forms arecan be stained with Acid-fast stain but not recommended because it is considered a narrow spectrum stain for fungi.
- Why do we Heat the slide full carbolfuschin during Ziehl Neelsen stain
- What is the name of the Ziehl neelsen counter’s stain
- List 04 samples that can be stained using Zielh Neelsen
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