Acid-fastness

Acid-fastness

Acid-fastness is a physical property of certain bacterial and eukaryotic cells, as well as some tissues, that makes them resistant to decolorization by acids during staining procedures. This property is primarily used in the identification of Mycobacterium species, including the pathogen Mycobacterium tuberculosis, which causes tuberculosis.

Mechanism

The acid-fast property is due to the presence of mycolic acids in the cell walls of acid-fast organisms. These long-chain fatty acids make the cell wall waxy and impermeable to many chemicals, including acids. As a result, once the cells are stained with a dye such as carbol fuchsin, they retain the dye even when treated with acid-alcohol solutions.

Staining Techniques

The most common staining technique used to identify acid-fast bacteria is the Ziehl-Neelsen stain. This method involves staining the cells with carbol fuchsin, heating the slide to allow the dye to penetrate the waxy cell wall, and then decolorizing with an acid-alcohol solution. Acid-fast cells retain the red color of the carbol fuchsin, while non-acid-fast cells do not.

Another method is the Kinyoun stain, which is a cold staining method that does not require heating. The Auramine-rhodamine stain is a fluorescent staining technique that is also used to identify acid-fast bacteria.

Clinical Significance

Acid-fastness is an important diagnostic feature in clinical microbiology. The ability to identify acid-fast bacteria is crucial for the diagnosis of diseases such as tuberculosis and leprosy, which are caused by Mycobacterium leprae.

Related Organisms

In addition to Mycobacterium species, other genera such as Nocardia and Cryptosporidium also exhibit acid-fastness. These organisms can be identified using similar staining techniques.

Related Pages

• Mycobacterium tuberculosis
• Ziehl-Neelsen stain
• Tuberculosis
• Leprosy

Gallery

• 
  Mycobacterium tuberculosis stained with Ziehl-Neelsen stain

Acid-fastness

•