Question

1. Describe several advantages of differential staining procedures compared with simple staining techniques. 2. Give the purpose of each of the following reagents in a differential staining procedure: a. Primary stain b. Counter stain c. Decolorizing agent d. Mordant 3. Why is it important for the counter stain to be a lighter color than the primary stain? 4. You have done gram staining for a gram positive bacteria, but at the end you observed pinkish-red bacteria under microscope, what was the possible error? 5. You have a mixed of gram positive and negative bacteria, but at the end you have just purple cells, what was the problem? 6. A student gram stains gram negative bacteria, but at the end the cells are clear, do you have any explanation?

Answer 1

Question

1. Advantages of differential staining procedure over simple staining procrdure are:

I. Differential stain is useful to differentiate between different microbes that simple staining cannot do.

II. Differential stain is useful to differentiate between gram-positive and gram-negative bacteria.

III. Differential stain can differentiate different physical characterstics of the microbes. For example, cell wall of bacteria can be differentiated.

2.

a. Primary stain: to impart color to all the cells.

b. Counter stain: make the stained cells visible in the microscope.

c. Decolourizing agent: used to dehydrate the cell wall

d. Mordant: increase the cell affinity for the stain

3. Counter stain is lighter than primary stain because cells could be differentiated from the background.

4. The mordant or iodine is not added during the experiment that allow dye to go out of the cell.

5. The decolorizer was not added during the experiment that made cells purple in color.

6. The failure to apply safranin lead to the no coloring of the cell and made it clear.