Microorganisms are invisible to the naked eye. Therefore for the purpose of studying, they are cultured. Staining will kill microorganisms. Dyes are used to staining and smears are prepared. Most commercial dyes are salts in which one of the ions are colored. Eg: Methylene blue (MBCl).
MBCl = MB+ + Cl-
There are two kinds of dyes. Basic dyes and acidic dyes. Methylene blue, crystal violet, carbon fuchsin are basic dyes in which the positive ion gives the color. Basic dyes will stain the acidic components of the cell such as the nucleus.
Salts in which the negative ion gives the color are called acidic dyes, stains basic components of the cell such as cytoplasm and granules. Eg: Safranin, Congored, and Acid Fuchsin.
Methods of Staining
- Simple staining
A single dye application.Mainly basic dyes such as Methylene blue, crystal violet, carbolfuchsin used.
- Differential staining
Use more than one dye. This method distinguishes one type of cell from another.
Eg: Gram stain, KOH procedure (gram reaction).
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