Which staining property is used to identify Mycobacterium tuberculosis in tissue sections?

• A. Gram staining
• B. H&E
• C. Ziehl-Neelsen
• D. Acid-fast staining

Answer: (D)

The main idea is acid-fastness. Mycobacterium tuberculosis has a waxy, lipid-rich cell wall containing mycolic acids, which makes the organism resist decolorization with acid-alcohol. Because of this, it retains the red dye of an acid-fast stain even after decolorization, allowing it to be visualized in tissue sections as bright red against a counterstained background. The classic method to demonstrate this property is the Ziehl-Neelsen stain, which uses carbol fuchsin to penetrate the cell wall and then acid-alcohol to decolorize; the acid-fast organisms remain colored. Gram staining isn’t reliable for MTb due to the waxy wall, and routine H&E staining shows tissue structure but not consistently the bacteria. So identifying Mycobacterium tuberculosis in tissue sections hinges on its acid-fast staining property.