In 1884, Danish microbiologist Hans Christian Gram discovered that crystal violet irreversibly stained certain bacteria but can be washed from others. The Gram stain technique identifies bacteria as gram-positive (the stain is retained) or gram-negative (the stain is washed away.)
Gram found that his stain worked for visualizing a series of bacteria associated with disease such as the “cocci of suppurative arthritis following scarlet fever.” He found, however, that Typhoid bacilli were easily decolorized after the treatment with crystal violet and iodine, when ethanol was added. We now know that those organisms that stained blue/violet with Gram’s stain are gram-positive bacteria and include Streptococcus pneumoniae (found in the lungs of those with pneumonia) and Streptococcus pyogenes (from patients with scarlet fever) while those that were decolorized are gram-negative bacteria such as the Salmonella Typhi that is associated with Typhoid fever.
Today, the Gram stain is still considered the “gold standard.” In this short video below, Hardy Diagnostics demonstrates how to perform the perfect Gram stain.
By Megan Roesner
Clinical Marketing Coordinator