Gram Staining

Question 1

What is Gram Positive

Answer 1

If you see a purple stain when ob-
serving the smear under a micro-
scope it shows that Gram-positive
bacteria are present

Question 2

What is Gram Negative

Answer 2

If the smear has retained the pink
safranin stain, which shows that
Gram-negative bacteria are pre-
sent
This is because their thinner
cell walls and lipid membranes
allow ethanol (applied during the
method) to wash off all the crystal
violet purple stain and then re-
tain the pink safranin stain

Question 3

What stains are used in Gram staining for the bacterial smear

Answer 3

Crystal Violet
Safranin

Question 4

Briefly explain how to carry out Gram Staining

Answer 4

1) Application of crystal violet (purple dye)
2) Application of iodine (mordant)
3) Alcohol wash (decolorization)
4) Application of safranin (counterstain)
5) View under a microscope

Question 5

Difference between gram negative bacteria and gram positive bacteria

Answer 5

Gram-positive bacteria are surrounded by a single thick peptidoglycan cell wall and are therefore termed monoderms
Gram-negative bacteria have a much thinner peptidoglycan cell wall, but in addition they have an outer membrane