This kit allows you to differentiate bacteria using the Gram staining method. It includes Hucker's crystal violet, safranin counterstain, Gram's iodine stain, ethyl alcohol, 12 plain microscope slides, 100 coverslips, medicine dropper, and our own study guide. Grades 7-12.
Test different types of bacteria, such as Gram-positive Bacillus cereus and Gram-negative Rhodospirillum rubrum and compare how the stains differ.
What is Gram staining? Hans Christian Gram, a Danish bacteriologist, discovered that bacteria could be divided into two different groups - one that retained a stain ("gram-positive") and one that didn't ("gram-negative"). His method for identifying these two groups became the first step in any bacterial identification process.
Gram's method of staining has several steps: a sample of bacteria is placed on a microscope slide, then is stained and "fixed" with iodine. The slide is then washed in a solvent to
"decolorize" the first stain. Gram-positive cells will retain the stain even
after being washed in the solvent, but the stain will be removed from the
gram-negative cells. This is because the cell walls of gram-negative cells
contain more lipids (fatty substances). The
solvent dissolves the lipid layer, allowing the color to be drawn from the
cell. The solvent causes the gram-positive cell wall to
dehydrate, closing the pores and trapping the stain inside the cell. In the
last step, the gram-negative cells are stained a different color, to contrast them from the gram-positive cells.
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