After ethanol treatment Gram negative bacteria can be visualised

Q. After ethanol treatment Gram negative bacteria can be visualised

A

Only by counter staining with Safranine

B

In violet colour of Crystal violet

C

Only by addition of iodine solution

D

None of these

Solution:

In Gram staining, the decolorizing agent, usually ethanol is added to the solution which consists of cells.
Cells that have thick peptidoglycan layers in their cell walls are much less affected by the decolorizing agent; they generally retain the crystal violet dye and remain purple.
However, the decolorizing agent more easily washes the dye out of cells with thinner peptidoglycan layers, making them colorless.
Finally, a secondary counterstain, usually safranin, is added.
This stains the decolorized cells pink.

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