Question

welcome back to the lab! what a journey huh? before we move on with the sample analysis, lets do a recap.
what are the four reagents used in the gram stain?
a) crystal violet, safranin, 95% ethyl alcohol, hydrogen peroxide
b) crystal violet, safranin, 95% ethyl alcohol, iodine
c) crystal violet, safranin, 90% methyl alcohol, iodine
d) crystal blue, safranin, 95% ethyl alcohol, iodine

Explanation:

Gram - staining is a common method in microbiology. The steps of Gram - staining are:

1. Primary staining: Crystal violet is used as the primary stain. It stains all bacteria (both Gram - positive and Gram - negative) purple.
2. Mordant: Iodine is used as a mordant. It forms a crystal violet - iodine complex within the bacterial cells.
3. Decolorization: 95% ethyl alcohol is used for decolorization. Gram - negative bacteria lose the crystal violet - iodine complex due to their thin peptidoglycan layer and lipid - rich outer membrane, while Gram - positive bacteria retain the complex because of their thick peptidoglycan layer.
4. Counter - staining: Safranin is used as a counter - stain. It stains the decolorized Gram - negative bacteria pink/red.

Hydrogen peroxide is not used in Gram - staining (it is used in catalase tests). Methyl alcohol is not the decolorizing agent in Gram - staining (ethyl alcohol is). Crystal blue is not the primary stain in Gram - staining (crystal violet is).

Answer:

B. Crystal violet, safranin, 95% ethyl alcohol, iodine