Question

Predict the effect on Gram-positive and Gram negative cells of the following "mistakes" made when performing a Gram stain. Consider each mistake independently.

A. Failure to add the iodine.
B. Failure to apply the decolorizer.
C. Reversal of the crystal violet and Safran in stains.

Answer 1

A. Failure to add iodine.

As iodine cross links with the crystal violet,so in its absence the crystal violet will come out of cell. This linking is helpful in to make the stain stay in the cell during decolorisation . So when we add safranin in its absence all the cells will appear pink and gram negative.

B. Failure to apply the decoloriser

If we dont apply decolouriser then everything will be purple. It is due to the crystal violet.

C. Reversal of crystal violet and safranin

In this case also everything will appear purple because during decolourisation the safaranin will come out of cell and iodine will bind to crystal violet only and hence give the purple coliur.