Performing Acid-Fast Bacillus (AFB) Staining

Introduction

Acid-Fast Bacillus (AFB) staining is a critical microbiological technique used to identify bacteria that possess a waxy cell wall, such as Mycobacterium tuberculosis. These bacteria resist traditional staining methods and require specialized stains to be visualized under the microscope.

Materials and Reagents Required

• Carbol Fuchsin (Primary Stain)
• Acid Alcohol (Decolorizer)
• Methylene Blue (Counterstain)
• Glass Slides
• Microscope

Procedure

1. Preparation of the Sample

Smear the specimen onto a clean glass slide and heat-fix it by gently passing it over a flame.

2. Primary Staining

Flood the smear with carbol fuchsin and heat the slide gently to enhance penetration.

3. Decolorization

Rinse the slide with acid alcohol to remove excess stain from non-AFB bacteria.

4. Counterstaining

Apply methylene blue to provide contrast against the background.

Interpretation of Results

AFB-positive organisms appear bright red against a blue background. This result indicates the presence of acid-fast bacteria.