What Is a Primary Stain?


Quick Answer

The primary stain is used in Gram staining to detect Gram-positive bacteria. The primary stain is a crystal violet color. When a bacteria is Gram-negative, it loses the primary stain and takes on the secondary stain of safranin.

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Full Answer

Differences in thickness of the peptidoglycan layer of the cell membrane of bacteria makes it possible to distinguish Gram-positive from Gram-negative bacteria. Bacteria that are Gram-positive have a thicker peptidoglycan layer and are able to retain the primary color of crystal violet.

Gram staining is a three-step process that involves primary staining, decolorizing to dehydrate the peptidoglycan layer and secondary staining to determine the type of bacteria.

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