Acid fast stain (Ziehl Neelsen's staining)
It is used for acid fast organism such as;
1. Micobacterium tuberculosis
2. Mycobacterium leprae
These organism are difficult to stain by ordinary staining method due to presence of high lipid content (mycolic acid) in their cell wall.
Bacteria are classified as;
1. Acid fast
2. Non acid fast
1. Acid fast
(Gram positive)
Acid fast bacteria resistant to decolourization by strong acid.
Acid fast organism are rich in lipid, higher alcohol and mycolic acid.
Appear red colour.
2. Non acid fast
(Gram negative)
Non acid fast bacteria easily decolourized by strong acid wash.
Appear blue/green colour.
For staining such organism ziehl-neelsen staining method is used called acid-fast staining.
Procedure of ziehl-neelsen staining
1. Prepare smear and fix it
2. Slide flooded with carbon fuschin and gently heat until steam arise, keep it for 3-5 minutes.
3. Wash under water
4. Apply acid alcohol for 1-2 minutes
5. Wash under water
6. Cover stain with methylene blue for 1 minute
7. Wash under water
8. Dry the slide
9. Acid fast bacilli retain red colour of carbol fuschin.
10. After 2 minute examine in oil immersion under microscope.
11. Non-acid fast bacteria appear green or blue in colour.
Observation and Report
Acid fast bacilli appear red in colour and non acid fast bacilli appear blue.
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