2. Aim of this lecture
To incorporate the basic knowledge on stain,
staining and applications of staining
After this lecture you should know
What is staining
Difference between the dye and stain
Components of stain
3. What is Staining?
It is the artificial coloration of a substance to
facilitate examination of tissue, microorganism or
other cells under microscope
4. What is the difference between stain and dye?
Stain
Used to stain
biological specimens
Pure form
Large molecular
structure
It contains pigment,
binder and carrier
material
Solubility is less
Dye
• Used as coloring
agent for general
purposes
• Crude form
• Small molecular
structure
• Pigment and carrier
• More soluble
6. History
Hans Christian Joachim Gram, Danish bacteriologist
and physician
Developed Gram staining technique in 1883 and
published his findings in 1884 in Friedlander’s Journal
Was working with respiratory disease in lung tissue
from cadaver at Municipal Hospital Berlin and his
accidental spillage of lugol’s iodine over lung tissue
sections led to the development of Gram Staining.
While examining the lung tissue from the patients who
had died of pneumonia, he observed that certain stains
were preferentially taken up and retained by bacterial
cell.
7. His initial work with this staining
process was performed on Klebsiella
pneumoniae and Streptococcus
pneumoniae.
He did not use a counter stain in his
procedure. It was a few years later, that
the German pathologist Carl Weigert
(1845-1904) from Frankfurt, added a
final step of staining with safranin.
8. Procedure
I. Primary stain- Crystal violet
II. Mordant- Gram’s Iodine
III. Decolorizer- Acetone or alcohol or mixture of
acetone alcohol
IV. Counter stain- Neutral red or Safranine
12. Principle of gram staining
Three hypothesis
a. Cell wall related
b. PH related
c. Magnesium ribonuclease related
13. a) Cell wall permeability hypothesis
Gram positive cell wall has thicker peptidoglycan layer as
compared to Gram negative cell wall .
Gram negative cell wall contains a thick layer of
lipopolysaccharide in their cell wall which is absent in
Gram positive bacteria .
During Gram staining a dye iodine complex (CVI complex) or
lake is formed within the cell wall after staining with crystal violet
and on subsequent treatment with iodine .This complex is
insoluble in water but soluble in alcohol.
Now when we add decolourizer (Acetone alcohol ), the dye iodine
complex is trapped inside the thick peptidoglycan layer of Gram
positive bacteria so they are not decolorized.
But outer lipopolysacharide layer of Gram negative cell wall is easily
dissolved by the decolourizer due to which dye iodine complex is
easily washed away from Gram negative cell.
14. b) Presence of magnesium ribonucleate
Magnesium ribonucleate present in Gram positive
bacteria has affinity for basic dyes. As a result Gram
positive bacteria take the color of crystal violet .
It has also been proved that Gram positive bacteria
become Gram negative upon removing this material.
15. c) pH hypothesis
Cytoplasmic pH of Gram positive bacteria is more
acidic (2-3) as compared to Gram negative
bacteria(4-5) and since the primary stain used
(crystal violet ) is basic in nature it develops more
affinity with the Gram positive cytoplasm .
The difference in pH is mostly due to presence of
Teichoic acid in the cytoplasm of gram positive cell,
which is absent in Gram negative cell.
16. Utility
Gram staining is a method of differentiating
bacterial species into two large groups (Gram-
positive and Gram-negative)
The Gram staining is almost always the first step in
the identification of bacteria
It is a valuable diagnostic tool in both clinical and
research settings, not all bacteria can be definitively
classified by this technique. This gives rise to Gram-
variable and Gram indeterminate groups as
well
17. Importance of gram staining
Important test for the rapid presumptive diagnosis of
infectious agent
To classify the bacteria as a Gram positive or Gram
negative
To study the morphology of bacteria
To study the arrangement of bacteria
To find out the evidence of capsule
To find out the evidence of spore
To find out the evidence of pus cells
To find out the evidence of epithelial cells
To find out the evidence of Yeast cells
18. Summary of this lecture
Gram staining was invented by Christian Gram
during 1884
Gram staining contains four components
crystal violet
iodine
alcohol
saffranin
Gram staining is generally used to classify the
microorganisms