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Acid Fast Techniques

Bacteria of the genus Mycobacterium possess waxy materials in their cell walls. They are difficult to stain by ordinary methods, and heat must be applied to force the dye molecules through to the cytoplasm. Once stained, however, the cells are not easily decolorized, even with alcohol solution containing 5% acid.

The organisms are said to be acid resistant or acid-fast. Air dried heat fixed smears are heated while being stained with ZiehlNeelsen's Carbolfuchsin. The cells become bright red. The smear is then rinsed with acid alcohol decolorizer. During this time the acid fast bacteria remain red while other bacteria lose their color
.