Perform and Interpret Acid-Fast Bacillus (AFB) Staining

Introduction

Acid-Fast Bacillus (AFB) staining is a critical microbiological technique used to identify acid-fast bacteria, such as Mycobacterium tuberculosis. These bacteria resist decolorization by acid alcohol, making them distinguishable under a microscope.

Step-by-Step AFB Staining Procedure

1. Sample Preparation

• Prepare a bacterial smear on a glass slide.
• Allow it to air dry and heat-fix the smear.

2. Primary Staining with Carbol Fuchsin

• Cover the smear with carbol fuchsin dye.
• Heat gently until steam forms but avoid boiling.
• Let the dye sit for 5 minutes, then rinse with water.

3. Decolorization

• Apply acid alcohol to remove excess stain.
• Rinse the slide to prevent over-decolorization.

4. Counterstaining

• Flood the slide with methylene blue for 1 minute.
• Rinse with water and air dry.

Interpreting AFB Staining Results

Positive Result

Acid-fast bacteria appear bright red due to retention of carbol fuchsin dye, signifying the presence of Mycobacterium species.

Negative Result

Non-acid-fast organisms appear blue due to methylene blue counterstaining, indicating the absence of acid-fast bacteria.

Importance of AFB Staining

This staining technique is essential for diagnosing tuberculosis and other mycobacterial infections. It ensures rapid identification, aiding in early treatment.