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Components of Gram Stains

The Gram stain, which was developed by a Dutch microbiologist in 1884, is a medical test used in differentiating between two different lung conditions. The test looks at the cells in the lungs and determines which type of bacteria is present based on the reactions to certain components injected into the tissue.

  1. Violet Dye

    • The first component added to a Gram stain lab is the primary stain. This stain is typically some type of violet dye, such as crystal, methyl or Genetian violet. The purpose of this dye is to change the color of the bacteria cells. However, this component is not used by itself. After this component is added to the cells, the second component must also be added before making preliminary observations. Without the second component, the dye is less likely to color the cells.

    Iodine

    • At the same time the dye is added to the cells, the lab technician also adds iodine to the mix. The iodine works with the violet dye to create a stronger hold on the cells that retain the color. In this stage of the test, all cells will acquire the purple-brown color of the violet-iodine mix. At this point, there is little differentiation between a test that is positive versus one that is negative.

    Ethyl Alcohol or Acetone

    • After the cells have been dyed with the combination of violet dye and iodine, etyhl alcohol, acetone or a combination of the two are added to decolorize the cells. In cells that are negative, the decolorization solution dissolves the outer fatty layer of the cells. Because only the outer layer of all of the cells absorbs the dye, any negative cells are washed free of the color with this solution. However, Gram positive cells maintain their purple-brown color because the solution dehydrates the cells, closing the pores through which the dye can escape.

    Counterstain

    • Different labs use different types of counterstain as the last component of a Gram stain test. Some labs use fuchsin, while others use safranin instead. However, the fuchsin creates a darker, more easily seen color and is often preferred. The purpose of this second dye is to turn any negative cells to a pink color instead of the purple-brown from the violet dye and iodine combination. This helps the lab technician to see the differences clearly between the two types of cells. Once the lab technician administers the counterstain, he can differentiate between the two cells, as well as see size and shape clearly.

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