Principle
Mycobacteria (AFB/Acid Fast Bacteria) are difficult to stain due to high lipid and wax content in their cell walls.
This differential staining technique is useful for identification of the tubercle bacillus, other Mycobacteria and Nocardia, which depends on the chemical composition of the bacterial cell wall. Because of the difficulty in staining these organisms with ordinary dyes, basic dyes in the presence of controlled amounts of acid are used.
Generally, heat must be applied during the staining procedure, or wetting agents must be used, to aid dye penetration. Organisms exhibiting the property of acid-fastness, once stained, are not easily decolourized by alcohol.