Questions:
A. What is a differential stain? How is it different from a simple stain?
A differential stain is a stain that distinguishes between gram-positive and gram-negative bacteria. Bacteria that stain purple are considered gram-positive and bacteria that stain pink are considered gram-negative.
B. What is the difference between gram-positive and gram-negative cell walls?
Gram-positive cell walls are thick and have many interconnecting layers of peptidoglycan. Gram-negative cell walls are thin and have only one layer of peptidoglycans that are two or three layers thick.
C. What is the purpose of crystal violet in the Gram’s stain procedure?
The crystal violet increases the contrast of both gram-negative and gram-positive bacteria making them look purple.
D. What is the purpose of iodine in the Gram’s stain procedure? (What is a mordant?)
The purpose of iodine in Gram’s stain procedure is it helps set the stain by forming an insoluble crystal violet-iodine complex. It helps keep the crystal violet to the cell.
E. What is the purpose of acetone-alcohol in the Gram’s stain procedure?
The purpose of acetone-alcohol is it is a decolorizer that distinguishes between gram-negative and gram-positive. Only the gram-positive bacteria will keep the crystal violet-iodine complex. Gram-negative bacteria will not keep the color and the decolorizer will wash off the stain.
F. What is the purpose of safranin in the Gram’s stain procedure?
The safranin in the Gram’s stain is a basic dye that directly stains the gram-negative bacteria that have become decolorized. The gram-positive bacteria are already stained and are not affected. It gives gram-negative bacteria a pink red’ish color
G. Why do gram-positive cells stain purple?
Gram-positive cells stain purple because they keep the crystal violet-iodine complex in their cell walls. The crystal violet is a positive