Final answer:
The modern method for staining acid-fast bacteria typically involves the Ziehl-Neelsen or Kinyoun staining techniques, using carbolfuchsin as the primary stain and differentiating cells based on the presence of mycolic acids in their cell walls.
Step-by-step explanation:
The modern method for staining acid-fast bacteria involves using differential staining techniques, specifically acid-fast staining. This diagnostic tool differentiates bacteria based on the presence of mycolic acids in their cell walls. The Ziehl-Neelsen and Kinyoun methods are the two primary techniques for this purpose, both using carbolfuchsin as the primary stain. In the Ziehl-Neelsen technique, heat is applied to allow the stain to penetrate the waxy cell wall, whereas the Kinyoun method does not require heat.
During the staining process, a heat-fixed smear is covered with carbolfuchsin and heated over a steaming water bath. The heat assists in the absorption of the dye by 'melting' the waxy cell wall. After cooling, the smear is decolorized with acid-alcohol. Acid-fast bacteria resist this decolorization and maintain the pink color of the primary stain, while non-acid-fast cells lose the pink stain and are then counterstained with methylene blue, which renders them blue.