All of the Following are Common to Both the Gram

Question

All of the following are common to both the Gram stain and the acid-fast stain EXCEPT
A) primary stain.
B) counterstain.
C) a decolorizing agent.
D) a chemical mordant.
E) a decolorizing agent and a counterstain.

Accepted Answer

Both the Gram stain and acid-fast stain use a primary stain (Crystal violet and Carbol fuchsin respectively), a decolorizing agent (either ethanol or acid-alcohol) and a counterstain (Safranin and Methylene blue respectively). However, only the Gram stain uses a mordant (Gram's iodine) to enhance the retention of the primary stain, while the acid-fast stain uses heat as a mordant to drive the primary stain into the acid-fast bacteria. Therefore, the correct answer is D.