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Ubile Medical Laboratory-UML, Ubile Medical Laboratory UML Office, Mbiama (2025)

29/11/2025

Bact

29/11/2025

Loa loa

28/11/2025

Ziehl–Neelsen (AFB) Stain
1. Objective:
The objective of the test was to detect acid-fast bacilli (AFB) such as Mycobacterium tuberculosis in clinical samples (e.g., sputum).
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2. Principle:
The test was based on the principle that acid-fast organisms contain mycolic acid in their cell walls, making them resistant to decolorization by acid–alcohol.
When stained with carbol fuchsin and heated, the dye penetrated the waxy cell wall.
After decolorization with acid–alcohol, only acid-fast bacteria retained the red stain, while non-acid-fast organisms were counterstained blue with methylene blue.
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3. Materials:
• Heat-fixed smear on glass slide
• Carbol fuchsin stain
• Acid–alcohol (3% HCl in ethanol)
• Methylene blue
• Bunsen burner or hot plate
• Wash bottle with water
• Microscope
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4. Procedure:
1. A thin smear was prepared on a clean slide and heat-fixed.
2. The smear was flooded with carbol fuchsin.
3. The slide was gently heated until steam rose (without boiling) for about 5 minutes.
4. Excess stain was washed off with water.
5. The smear was decolorized with acid–alcohol until no more red color flowed out.
6. The slide was washed again with water.
7. Methylene blue was applied as counterstain for 1–2 minutes.
8. The slide was washed, air-dried, and examined under oil immersion.
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5. Result:
• Positive: Bright red, rod-shaped AFB seen against a blue background.
• Negative: No red bacilli observed; background stained blue.
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6. Uses:
• Diagnosis of tuberculosis (primary use).
• Detection of Mycobacterium leprae and other acid-fast organisms.
• Monitoring response to TB treatment.
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7. Consultation:
Results were interpreted by a trained laboratory professional. Positive findings were immediately communicated to the clinician