Microbiology Case

Labset Two Worksheet

1. What is differential staining? How does it differ from simple staining? (2)

A differential stain can distinguish between two types of bacteria because the bacteria can differ from one another physically and chemically to react differently to a staining procedure.

A simple stain is dependent upon the fact that bacteria different chemically from their surroundings and can be stained with their environments.

2. What are the differences between gram positive and gram negative cell walls? (2)

Gram positive and negative just refers to how a bacteria is going to react to a gram stain. If is gram positive, it takes the initial stain and will be purple and if it is negative, that means it did not take the initial stain and is pink.

The difference between the two is going to be seen in the outer casing of the bacteria. Gram positive bacteria has a thick layer of peptidoglycan that the stain can penetrate whereas the gram negative bacteria has a thin layer of peptidoglycan on the outside that prevents the initial stain from penetrating.

3. What is a mordant? What serves as a mordant in the gram stain protocol? (2)

A mordant is a substance that combines with a stain or a dye and fixes or sets in a material. Iodine serves as a mordant in the gram stain protocol because it sets the purple dye, thus making it set in better.

4. Why do gram negative cells stain pink? Gram positive cells purple? (2)

The way the cells stain mainly has to do with the outer layer of the cell. Since gram positive bacteria has such a thick layer of peptidoglycan, it absorbs the gram stain, therefore it stains purple.

Gram negative bacteria has a higher lipid content and contains a thinner layer on the outside which does not allow for everything to pass through it, including the gram stain, which causes it to stain pink.

5. What is measured