Question

How might the results of the Gram stain be impacted if the primary and secondary stain were switched?

(Microbiology)

Answer 1

During the Gram staining procedure:

Crystal violet is the primary stain. All bacteria get stained purple.

Safranin is the secondary stain.

Between the two staining, there is an alcohol wash, which removes crystal violet stain from Gram negative baceria. The stain is however retained by the Gram positive bacteria, Such bacteria have a thick peptidoglycan layer in their cell wall, which allows them to retain the stain and thus appear purple. Gram negative bacteria appear pink, due to counter stain safranin, added later.

If the two stains are switched. All bacteria will be colored pink initially by safranin. Alcohol will destain Gram negative bacteria. On adding crystal violet now as the secondary stain, Gram negative will get purple color. Gram positive will remain pink.