Acid-fast stain

Definition

Acid-fast stain is a differential staining technique used to identify acid-fast bacteria, such as Mycobacterium species. It differentiates bacteria based on the properties of their cell walls.

5 Must Know Facts For Your Next Test

1. Acid-fast stain primarily identifies Mycobacterium tuberculosis, the causative agent of tuberculosis.
2. The Ziehl-Neelsen method and the Kinyoun method are two common techniques for performing an acid-fast stain.
3. Acid-fast bacteria retain the primary stain (carbol fuchsin) even after being treated with a decolorizing agent (acid-alcohol).
4. Non-acid-fast cells will lose the primary stain when decolorized and will take up the counterstain (methylene blue or brilliant green).
5. The high mycolic acid content in the cell walls of acid-fast bacteria is responsible for their staining characteristics.

Review Questions

• What type of bacteria can be identified using an acid-fast stain?
• Name two methods commonly used to perform an acid-fast stain.
• Why do acid-fast bacteria retain the primary stain even after treatment with acid-alcohol?

Related terms

Differential Staining:

A technique that uses more than one chemical stain to differentiate between different microorganisms or structures.

Mycobacterium:

A genus of Actinobacteria, which includes pathogens known to cause serious diseases in mammals.

Ziehl-Neelsen Stain: A specific method of acid-fast staining that uses heat to help dye penetrate waxy cell walls.