Differential stains: are more complex, using 4 reagents (the order is important), and help to separate organisms/cells; and/or help to visualize structures (organelles) such as flagella, capsule, spore, or nucleus.
The primary stain is the first reagent and its purpose is to colorize all cells.
The mordant is the second reagent which helps to increase the contrast and color intensity of the primary stain.
The decolorizing agent is the third reagent. Depending on what you’re trying to stain, the decolorizing agent selectively (e.g. the cell or cellular structures/organelles) removes the color from the primary stain.
The counterstain is the fourth reagent and is a contrasting stain to the primary stain. The counterstain will add color to that which the decolorizing agent removed. The counterstain will not bind to those cells/structures that retained the primary stain).
Clinical significance. The Gram stain is the predominant differential stain—especially used in the clinical setting. It quickly assesses organisms that fall into one of two categories—Gram positive (purple) and Gram negative (pink/reddish). Please visit this link for more details on the Gram stain.
Summary of procedure.
- Primary stain.
- Mordant.
- Decolorizing agent.
- Counterstain.
Please visit this link for more details on the Gram stain.
Reference
Cappuccino, J. G., & Welsh, C. (2018). Microbiology: A laboratory manual.
