Question

In the Gram staining procedure, all the bacterial cells get stained with
a) Mercuric chloride
b) Crystal Violet
c) Malachite green
d) Safranin

Answer 1

Hint: Gram staining is a technique to understand whether the bacteria are gram positive or gram negative bacteria. It distinguishes two types of bacteria on the basis of their cell wall composition.

Complete answer:
This staining procedure was developed by Hans Christian Gram. If the bacterium gets stained by this staining procedure, it is called gram-positive bacteria.

In this method, bacteria are stained with crystal violet, a primary stain. The process involves the heat fixing of the bacteria smear, followed by crystal violet staining. In order to strengthen the bond between crystal violet and cell wall components, iodine solution is added. Hence only gram positive bacteria takes up the violet color. In such a situation a counter stain such as safranin is added so the other bacteria could be identified.
Considering the above method, it is obvious that option b- crystal violet will be the correct choice.

Additional information:
Outside the gram-positive bacterial cell is a cell wall which is made up of peptidoglycans. It is rich in Teichoic acid. The cell wall of gram-negative bacteria is relatively thinner and teichoic acid is absent. Lipopolysaccharide layer is present outside peptidoglycan layer in gram-negative bacteria.
When bacteria are stained with crystal violet, all get stained purple. On washing with acetone or alcohol, the gram positive bacteria retain the purple color due to the peptidoglycan layer. However, the gram-negative bacteria are unable to do so because they lack such a thick peptidoglycan layer. Gram negative bacteria have extra lipopolysaccharide layer outside peptidoglycan layer. This layer takes up safranin stain and hence they appear red.

Note: The essence of the gram-staining technique lies in different cell wall composition of the bacteria. The thick peptidoglycan layer outside the gram positive bacterial cell helps the cell to retain the violet color which is otherwise washed away after ethanol wash.