Question

both crystal violet and safranin are basic stains and may be used to do simple stains on gram-positive and gram-negative cells. This being the case, explain how they end up staining Gram-positive and gram-negative cells differently in the gram stain

Answer 1

Answer:

Both the stain which is used in gram staining may be used to do simple stains on gram-positive and gram-negative cells but gram-positive bacteria end beings stained violet and gram-negative being stained pink because of the composition of their cell wall.

As the gram-positive bacteria have an outer thick layer of peptidoglycan it is not decolorized after destaining step and the mordant iodine also helps it to do that but as the gram-negative bacteria have outer LPS layer in cell wall so it get decolorized after destaining as alcohol in destaining step degrades some LPS layer.

So after counter staining the gram-negative bacteria appears pink and gram-negative bacteria retain crystal violet so they appear purple.