Counterstain

A counterstain is a stain with colour contrasting to the principal stain, making the stained structure easily visible using a microscope.

Gram-positive anthrax bacteria with counterstained white blood cells

Examples include the malachite green counterstain to the fuchsine stain in the Gimenez staining technique and the eosin counterstain to haematoxylin in the H&E stain. In Gram staining, crystal violet stains only Gram-positive bacteria, and safranin counterstain is applied which stains all cells, allowing the identification of Gram-negative bacteria as well. An alternative method uses dilute carbofluozide. Counterstains are sometimes used to separate animals from organic detritus in microbiology studies.