THE GRAM STAIN Flashcards
What is the Gram stain used for?
to differentiate types of bacteria depending on their abilities to retain a particular stain (differential staining technique)
What is the process of gram staining?
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
What is the function of a mordant?
a substance that fixes the primary stain
Are gram positive easily decolourized and will retain the purple stain?
No
Are gram negative decolourized with 95% ethyl alcohol?
Yes they are stained by safranin and turn red/pink
Why do gram-positive cells more than 24 hours old stain gram-negative?
because of their peptidoglycan layer, it tends to deteriorate after a certain period of time
If the mordant is not added when performing the stain, what would be the gram reaction?
primary stain will be lost and all gram stains will be pink
What would be the appearance of all cells if the decolourizer was not added? smear was over-decolourized?
Purple. and Red.
