AAT Bioquest

What is the difference between negative and positive staining?

Posted March 16, 2023


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. 

Additional resources

Optimizing fresh specimen staining for rapid identification of tumor biomarkers during surgery

Gram Staining

MycoLight™ Bacterial Viability Assay Kit

Methylene Blue Azide