Question

Why is gram staining done?

Answer 1

Gram staining:

1. Gram staining is a staining technique performed to identify bacteria based on their membrane characteristic.
2. It helps to differentiate between gram-positive and gram-negative bacteria.
3. Gram-positive bacteria are bacteria with the presence of a peptidoglycan layer that takes up the primary crystal violet stain.
4. The first step in the staining process is to add the crystal violet stain which is taken up as the primary stain by the peptidoglycan layer.
5. Then Iodine solution is added which acts as a gram's mordant to fix the stain.
6. 95% ethyl alcohol is added to wash off the remaining stain.
7. In the last step, the counter stain (safranin) is added to change the color of cells other than crystal violet.
8. Whereas gram-negative bacteria are devoid of the thick peptidoglycan layer, hence unable to retain the primary crystal stain and take up the secondary counter stain.
9. Hence, this staining procedure helps us to differentiate between bacteria that take up the primary stain (gram-positive) because of the presence of the peptidoglycan layer and bacteria that absorb the counter stain (gram-negative) and are unable to take up the primary crystal violet stain due to the absence of peptidoglycan layer.
10. This procedure thus helps us in distinguishing and categorization of bacteria.