Direct preparation of Gram staining

Gram stain is probably one of the most commonly used staining procedures used in the field of microbiology. It is one of the differential stains that are used to characterize bacteria in one of two groups: either gram positive bacteria or gram negative bacteria.

The staining involves 3 major steps/processes that include;

  • Staining with crystal violet (a water soluble dye),
  • De-colorization (using ethanol/acetone),
  • Counterstaining (using Safranin),

Due to the differences in the thickness of the peptidoglycan layer on the cell walls of these bacteria, gram positive bacteria will retain the crystal violet stain after the de-colorization process using ethyl alcohol/acetone.

After staining the sample with crystal violet, ethyl alcohol is used to decolorize the sample. It achieves its purpose by dehydrating the peptidoglycan layer by tightening and shrinking it. In doing so, large crystal violet cannot penetrate the tightened layer of peptidoglycan, and hence it is trapped in the cell wall of gram positive bacteria.

On the other hand, the outer membrane of the gram negative cells cannot retain the crystal violet iodine complex and hence the color is lost.

  • Applied in various samples
  • We perform the test daily