The cell walls of Mycobacteria are made up of waxy substance, Mycolic acid that Is relatively Impermeable to ordinary staining techniques. But, by application of heat and a mordant (phenol), the cell can be stained The purpose of heating is to soften the waxy material of the cell wall and allow the stain to enter the cell. Basic fuchsin is more soluble in phenol and phenol is a better solvent for lipids and waxes.
because species of Mycobacteria are having thick mycoloic acid which can't be easily stained with ordinary staining techniques.
The acid-fast stain is a differential stain used to identify acid-fast organisms such as members of the genus Mycobacterium .
Acid-fast organisms are characterized by wax-like, nearly impermeable cell walls; they contain mycolic acid and large amounts of fatty acids, waxes, and complex lipids. Acid-fast organisms are highly resistant to disinfectants and dry conditions.
Because the cell wall is so resistant to most compounds, acid-fast organisms require a special staining technique. The primary stain used in acid-fast staining, carbolfuchsin, is lipid-soluble and contains phenol, which helps the stain penetrate the cell wall. This is further assisted by the addition of heat. The smear is then rinsed with a very strong decolorizer, which strips the stain from all non-acid-fast cells but does not permeate the cell wall of acid-fast organisms. The decolorized non-acid-fast cells then take up the counterstain.
Mycobacteria possess thick waxy cell wall rich in mycolic acid. This makes it difficult to be stained using Gram's techniques. But with the use of carbon fuschen,the cell wall can be stained using acid-fast technique
The waxy mycolic acid containing cell wall of mycobacteia are relatively impermeable to ordinary staining techniques. They can be stained by aniline dyes using drastic measures such as application of heat and phenol. Heat softens the wax in the cell wall and allows the stain (basic fuchsin) to enter. The fuchsin dye is more soluble in phenol than in water or alcohol. Phenol in turn is more soluble in lipids or waxes, thus the dye-phenol mixture enters the cell. Once stained, it resists decolourization by weak mineral acid (20% H2SO4). This is due to the fact that phenol-dye mixture is more soluble in waxes of the mycobacteria than the acid or alcohol. This way phenol acts as a mordant. While the mycobacteria retain the primary stain (pink), the background material gets decolourized and takes up the counterstain (methylene blue).
They have an abnormally high percentage of lipids in the cell. contain mycolic acid in their cell wall and are relatively resistant to drying and to disinfectants. They retain the primary dye, carbolfuchin and appear red when examind microscopically. The relatively impermeable, waxlike cell walls partially account for the acidfastness of certain bacterial cells.
They contain a waxy, granular material which makes it difficult for them to be stained and once stained, they are not decolorized by acid.
Dear Al-Jammal
The reason is due to high lipid content in the cell wall of Mycobacterium tuberculosis. It is consist of Fatty acid, mycolic acid and wax. This fatty barriers make tubercle bacilli is resistant to 20% of Mycobacterium tuberculosis. Regard
Carbol Fuchsin forms a complex with Mycolic Acid in the mycobacterium cell wall during the staining process. This complex resist decolourisation with acid or acetone, hence acid-fast
Mycobacteria are called acid-fast because they resist decolorization with acid alcohol due to the nature of their complex cell wall.
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