Acid-fast staining is done for –

✅ Explanation: Acid-fast staining is a technique used to identify bacteria with a waxy cell wall, like those in the genus Mycobacterium. This staining type is resistant to acid decolorization, hence termed acid-fast.
Additional Information:● Acid-fast stain: also known as the Ziehl-Neelsen stain.● This test determines if a sample of tissue, blood, or body fluid is infected with bacteria that cause tuberculosis and other illnesses.
Principle of Acid-Fast Staining:● Mycobacteria and Nocardia resist simple stains but can be stained by heating with Carbol Fuchsin.● Heat drives the stain into the cell; once stained, they resist acid-alcohol decolorization, hence called acid-fast.● This acid fastness is due to high lipid content in their cell walls.● Mycobacterium leprae has weak acid fastness and causes leprosy.● They are hydrophobic and impermeable to Gram stains.
Application of Reagents on Cells:● Primary dye: Carbol fuchsin- Acid-fast: Red- Non-acid fast: Red● Decolorizer: Acid alcohol- Acid-fast: Red- Non-acid fast: Colorless● Counterstain: Methylene blue- Acid-fast: Red- Non-acid fast: Blue