Principle: Gram staining depends on bacterial cell wall &
cytoplasmic membrane. When bacteria are stained with crystal violet &
mordant with lugols
some bacteria resist decolorization by alcohol
& others do not. The bacteria which resist are called gram positive &
those which are decolorized are gram negative. Gram positive bacteria stain
blue & gram negative bacteria stains red.
Procedure:
1. Fixation: The slide is flamed 3-4 times on the opposite side
of the smear. Thus the smear is fixed.
2. Primary
staining: Crystal violet is coated
over the smear & kept for 1 minute. It is then washed with tap water.
3. Mordanting: lugols
is coated over the smear & kept for 1
minute. It is then washed with tape water. It is done to increase the
penetration power of lugols
.
4. Decolorization: It is done by alcohol & is continued till the
violet color comes out from the smear. The slide is then washed with tap water.
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