Question

During Gram's stain

• A. All bacteria whether Gram (+)ve or (-)ve, take crystal violet stain
• B. Only Gram +ve bacteria take crystal violet stain
• C. Only Gram (-)ve bacteria take crystal violet stain
• D. Gram (+)ve bacteria lose this stain after alcohol treatment and take red stain of safranin

Answer 1

The correct option is B Only Gram +ve bacteria take crystal violet stain

1. Gram staining distinguishes between the Gram-positive and Gram-negative bacteria on the basis of the composition of the cell wall.
   
2. Gram-positive bacteria have a thick layer of peptidoglycan which helps to retain stain.
   
3. The Gram-positive bacteria is first treated with Gram stain which is retained by them. After staining they are treated with alcohol to decolourize.
4. Decolorizing the cell causes this thick cell wall to dehydrate and shrink, which closes the pores in the cell wall and prevents the stain from exiting the cell.
   
5. When they are stained by saffranine, they are unable to take the stain and appears blue.
6. Gram staining bacteria take up the Gram stain but they are unable to retain them due to the thin layer of peptidoglycan.
7. When they are exposed to alcohol, decolourizer dissolves the lipids in the cell walls, which allows the crystal violet-iodine complex to leach out of the cells.
   
8. When stained with safranin, they take the stain and appears red in colour.

So, the correct answer is 'Only Gram +ve bacteria take crystal violet stain'.