Acid Fast organisms not Always Mycobacterium species


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

Principle of Acid fast stain (Ziehl Neelsen)
Principle of Acid fast stain (Ziehl Neelsen)

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).
Red (Acid fast bacilli) - Purple (Non acid fast)
Red (Acid fast bacilli) – Purple (Non acid fast)  

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.

Also read  Thiosulfate Citrate Bile Sucrose Agar ideal for vibrio species

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

We’ll Love to read and Answer your comment


Wikipedia acid fast


How useful was this post?

Click on a star to rate it!

Average rating / 5. Vote count:

No votes so far! Be the first to rate this post.

We are sorry that this post was not useful for you!

Let us improve this post!

About the Author: Arthur Westmann

DEFFE ARTHUR (AMOEBAMANN) is the founder and author of MLTGEEKS and MLTEXPO.He’s from Cameroon and is currently a Final year State Medical Laboratory Technician (MLT MA). Beyond lab works, he’s a passionate internet user with a keen interest in web design and blogging. Furthermore He likes traveling, hanging around with friends and social networking to do in his spare time.

You May Also Like


Leave a Reply

Your email address will not be published. Required fields are marked *