Question

Counter stain used in AFB Staining is :

• A. Methylene Blue
• B. Congo Red
• C. Carbol fuchsin
• D. Mordant

Answer 1

Answer:

A. Methylene Blue

AFB Staining (Acid-Fast Bacilli) Overview

• The primary technique used for detecting Acid-Fast Bacilli, such as Mycobacterium tuberculosis, is the Ziehl-Neelsen (ZN) staining method.
• These bacteria are termed 'acid-fast' due to the high concentration of mycolic acid in their cell walls, which makes them resistant to decolorization by acid-alcohol.

Steps of the Ziehl-Neelsen Method

1. Primary Stain: Carbol Fuchsin (a phenolic dye) is applied with heat to force the stain into the waxy cell wall.
2. Decolorization: Acid-alcohol (usually 3% HCl in ethanol) is used. Acid-fast organisms retain the red color of the primary stain.
3. Counter Stain: The final step involves applying a contrast stain to visualize non-acid-fast organisms.

Counter Stain Details

• Methylene Blue is the standard counter stain used in the Ziehl-Neelsen procedure.
• In the Kinyoun method (a 'cold' staining technique that does not require heating), Malachite Green or Methylene Blue is typically used as the counter stain.
• Purpose: It provides a contrasting background color, appearing blue or green, allowing the red, acid-fast bacilli to stand out clearly under microscopy.