What is the difference between negative and positive staining?

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

- Example of positive staining – Gram staining

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.