Question

Why are you asked to gram stain a mixture of gram positive and gram negative bacteria on the same slide?

Answer 1

Gram staining is a technique used to differentiate and classify bacteria based on their cell wall structure. By gram staining a mixture of Gram-positive and Gram-negative bacteria on the same slide, you can compare and contrast their staining reactions and overall characteristics.

Step-by-step explanation:

Gram staining is a technique used to differentiate and classify bacteria based on their cell wall structure. Gram-positive bacteria have a thicker peptidoglycan layer in their cell wall, while Gram-negative bacteria have a thinner peptidoglycan layer. The differences in cell wall composition allow for differential staining during the Gram staining process. Gram-positive bacteria retain the purple crystal-violet stain, appearing purple, while Gram-negative bacteria lose the crystal-violet stain and instead take up the red safranin counterstain, appearing pink.

In the case of a mixture of Gram-positive and Gram-negative bacteria, gram staining on the same slide can help determine the Gram stain reaction, as well as the cellular morphology and arrangement of both types of bacteria. By observing both types of bacteria in a mixed smear, it becomes easier to compare and contrast their staining reactions and overall characteristics.

Answer 2

The accuracy of the Gram stain is dependent on the integrity of the bacterial cell wall. Variety of things can influence the cell wall integrity. Suppose the cells have been roughly handled , gram positive cells will come out as gram-negative. If you de-colorize them for too long, Gram-positive cells will look like Gram-negative cells or if you do not decolorize enough, Gram-negatives will look like Gram-positives. Under these circumstances Gram-positive and a known Gram-negative on the same slide so that the results are reliable.