The acid-fast stain is a laboratory technique used to identify certain bacteria, particularly those in the genus Mycobacterium, which includes the pathogen that causes tuberculosis. This staining method highlights the unique waxy cell wall of these bacteria, making them resistant to standard staining procedures. In the acid-fast staining process, a primary stain, usually carbol fuchsin, is applied, followed by heat to help the dye penetrate the cell wall. Afterward, a decolorizing agent, typically acid-alcohol, is used. Bacteria that retain the stain despite this treatment are classified as acid-fast, while others are not.