THE GRAM STAIN
The gram stain
is the most widely used staining procedure in bacteriology
It is called a
differential stain
since it differentiates between gram-positive and gram-negative bacteria.
Bacteria that stain
purple
with the gram staining procedure are termed
gram-positive.and those that stain Pink
are said to be
gram-negative
gram staining procedure
The bacteria are stained with the basic dye
crystal violet
Both gram-positive and gram-negative
bacteria become directly stained and
appear purple after this step.
The bacteria are treated with
gram's iodine solution
Both gram-positive and gram-negative
bacteria remain purple after this step.
then added
)
( Gram's decolorizer )
(ethyl alcohol). This is the differential step.
Gram-positive bacteria retain the crystal
violet-iodine complex while gram-negative
are decolorized
Finally, the counterstain
) safranin(
Since the gram-positive bacteria are already
stained purple, they are not affected by the
counterstain. Gram- negative bacteria are
now colorless, become directly stained by
the safranin
gram-positive appear purple
gram-negative appear pink
(Primary stain)
Gram’s
Gram’s
Crystal Gram’s Alcohol Safranin
Gram’s
violet iodine
Crystal
1-Preparing the Slide for Staining then •
Heat-fix a smear
You do heat the slide to
ensure that it does not wash off during the
staining process
2-Stain with crystal violet for one minute
wash Gently with water
3-Stain with gram's iodine solution For
one minute then
Wash with water
•
4-Decolorize by adding gram's decolorizer(alchol »
Wash immediately with water
Stain withsafranin for two minutes •
wash with water
Dry and observe
•
What is the Gram stain reaction, cell morphology, and
cell arrangement seen here?
Answer: Gram-positive streptococcus
What is the Gram stain reaction, cell morphology, and cell
arrangement seen here?
Answer: Gram-negative bacilli