Test Catageory
فئة التحليل
Microbiology
Refrence Books
كتب مراجع
1. Bailey & Scott’s Diagnostic Microbiology
2. Laboratory Manual and Workbook in Microbiology
Skills Required
المهارات المطلوبة
1. Smear preparation
2. Staining technique
3. Decolorization control
4. Microscope operation
5. Organism identification
Video Resources
مصادر فيديو
Principle
The primary stain carbolfuchsin binds to all bacteria. The acid-alcohol acts as a decolorizing agent, removing the red carbolfuchsin stain from all bacteria except mycobacteria due to their waxy cell walls. The counterstain methylene blue is then applied to provide contrast to see the red-stained acid-fast bacilli.
Solutions & Equipments
1. New, clean slides
2. Sterile inoculation loops
3. Carbolfuchsin stain
4. Acid-alcohol decolorizer
5. Methylene blue counterstain
6. Light microscope
7. Immersion oil
Sample Type
Sputum
Bronchial specimens
Tissue biopsies
Cerebrospinal fluid
Pus
Urine
Procedure
1. Prepare a thin smear of specimen on a new clean slide and allow it to air dry completely
2. Fix smear by gently heating
3. Flood slide with carbolfuchsin; steam for 5 minutes
4. Rinse gently with water
5. Decolorize with acid-alcohol for 30 seconds
6. Rinse gently with water
7. Flood slide with methylene blue for 1 minute
8. Rinse gently with water and allow to dry
9. Examine slide under oil immersion – AFB appear red against blue background
Results
Presence of red, beaded, slightly curved acid-fast bacilli indicates a positive test suggestive of mycobacterial disease. Absence suggests a negative result.
Interpretation Positive: Presence of red stained mycobacteria indicates specimen is positive for acid fast bacilli like M. tuberculosis. Further testing should be done to confirm diagnosis. Negative: Absence of red stained mycobacteria indicates specimen is negative. However, a negative result does not definitively rule out mycobacterial infection.
Notes:
1. Use positive and negative control slides for each new batch of stains to ensure proper staining quality and procedure.
2. Do not over-decolorize, as this can lead to false negative results.
3. Check for appropriate microscope brightness and immersion oil quality.
4. Take precautions when handling potential mycobacterial cultures.
M. Sulieman
mohammad@mlsgaate.com
The acid fast bacilli (AFB) stain is a differential stain used to detect Mycobacterium species, including Mycobacterium tuberculosis.
