Negative and positive staining are two types of staining techniques that are differentiated based on their ionic properties.
Positive staining
- Positive staining colors the body of the cell.
- Dyes used in this technique are basic dyes, which have a positive charge.
- Before staining, the bacteria is smeared onto a slide and heat-fixed.
- Example of positive stain – Crystal Violet
Negative staining
- Negative staining colors the background surrounding the cell but not the cell itself. The result is a dark colored halo around a clear cell.
- Dyes used in this technique are acidic dyes, which have a negative charge.
- There is no need to prepare a bacterial smear or heat-fix the sample prior to staining.
- Example of negative stain - Nigrosin
- Example of negative staining - Capsule staining of Klebsiella pneumonia.
