THE GRAM STAIN

Question 1

What is the Gram stain used for?

Answer 1

to differentiate types of bacteria depending on their abilities to retain a particular stain (differential staining technique)

Question 2

What is the process of gram staining?

Answer 2

1 - it involves staining the fixed smear with a primary stain (crystal violet)
2 - apply Gram iodine (mordant)
3 - wash the stain with decolourizing agent (ethyl alcohol 95%)
4 - counterstaining with safranin

Question 3

What is the function of a mordant?

Answer 3

a substance that fixes the primary stain

Question 4

Are gram positive easily decolourized and will retain the purple stain?

Answer 4

No

Question 5

Are gram negative decolourized with 95% ethyl alcohol?

Answer 5

Yes they are stained by safranin and turn red/pink

Question 6

Why do gram-positive cells more than 24 hours old stain gram-negative?

Answer 6

because of their peptidoglycan layer, it tends to deteriorate after a certain period of time

Question 7

If the mordant is not added when performing the stain, what would be the gram reaction?

Answer 7

primary stain will be lost and all gram stains will be pink

Question 8

What would be the appearance of all cells if the decolourizer was not added? smear was over-decolourized?

Answer 8

Purple. and Red.