Ready to use Gram stains.
For use in the Gram’s Staining method for the initial differentiation of Gram Positive and Gram Negative bacteria.
Gram stain was originally devised by Christian Gram in 1884. The standard Gram’s staining method can be used to differentiate intact, morphologically similar bacteria into two groups. This is based on cell wall colour after employing the staining method. In addition, cell form, size and structural details are evident. This preliminary information can provide initial clues to the type of organism(s) present.
A Crystal Violet-Iodine complex forms in the protoplast of all organisms stained using the above procedure. After decolorizing, those organisms that are able to retain this dye complex are classified as Gram positive. Those organisms that are decolorized and take up the counterstain are classified as Gram negative.
Upon disruption or removal of the cell wall, the protoplast of Gram positive as well as Gram negative cells can be decolorized, and hence the Gram negative attribute lost. Therefore, the mechanism of the Gram stain appears to be related to the presence of an intact cell wall able to act as a barrier to decolorization of the primary stain. Generally, the cell wall is non-selectively permeable. It is theorized that during the Gram stain procedure, the cell wall of Gram positive cells is dehydrated by the alcohol in the decolorizer and loses permeability, hence it retains the primary stain. In the case of the cell wall of the Gram negative cells, due to a higher lipid content, the cell wall becomes more permeable when treated with alcohol, hence the primary stain is lost, allowing for the later counterstain to be taken.