The Ziehl-Neelsen stain is a special staining technique used in microbiology to identify certain types of bacteria, particularly the genus Mycobacterium, which includes the bacteria that cause tuberculosis. This method highlights the presence of mycolic acid in the cell walls of these bacteria, allowing them to be visualized under a microscope. In the staining process, a sample is first stained with a red dye called carbol fuchsin, followed by a decolorization step using acid-alcohol. Finally, a counterstain, usually methylene blue, is applied. This results in acid-fast bacteria appearing red against a blue background, making them easily identifiable.