Counterstain
Counterstain
Counterstain (pronounced: /ˈkaʊntərˌsteɪn/) is a staining technique used in histology and microbiology to enhance the contrast of the main stain.
Etymology
The term "counterstain" is derived from the Latin contra meaning "against" and the Old English stæn meaning "stain". It refers to the application of a second stain with a color contrasting to the principal stain, making the microscopic details of the specimen more visible and differentiated.
Procedure
In a typical counterstaining procedure, the specimen is first stained with a primary stain, then washed, and subsequently stained with a counterstain of a different color. The counterstain allows for the differentiation of different cell components or types of cells, as it reacts differently to different tissues or cells than the primary stain.
Common Counterstains
Some common counterstains used in histology and microbiology include:
- Eosin: This is a red dye used in H&E staining, a common staining method in histology. It counterstains the blue hematoxylin stain, staining cytoplasmic components and extracellular matrix pink.
- Safranin: This is a red dye used in the Gram stain procedure. It counterstains the purple crystal violet stain, staining Gram-negative bacteria red.
- Nigrosin: This is a black dye used as a negative counterstain in light microscopy, providing a dark background against which lighter objects can be viewed.
Related Terms
- Staining: The process of applying a dye or stain to a biological specimen to enhance its contrast under a microscope.
- Primary stain: The first stain applied in a multiple-staining procedure, which colors the principal structures or components of the specimen.
- Mordant: A substance used to set or stabilize stains in tissue.
- Decolorization: The process of removing excess primary stain from a specimen before applying the counterstain in a staining procedure.
External links
- Medical encyclopedia article on Counterstain
- Wikipedia's article - Counterstain
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