THE GRAM STAIN

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THE GRAM STAIN
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The gram stain
is the most widely used staining
procedure in bacteriology
It is called a differential stain 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
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• Gram-positive ? Purple
• Gram-negative ? Pink

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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.

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• The bacteria are treated with
• gram's iodine solution
• Both gram-positive and gram-negative
  bacteria remain purple after this step.

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• 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

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• 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

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• 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

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• 2-Stain with crystal violet for one minute
• with water Gently wash

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• 3-Stain with gram's iodine solution For one
  minute then
• Wash with water

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• 4-Decolorize by adding gram's decolorizer(alchol

Wash immediately with water
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• Stain withsafranin for two minutes

wash with water
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• Dry and observe

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Answer Gram-positive streptococcus
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Answer Gram-negative bacilli