THE GRAM STAIN

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

Gram-positive  Purple Gram-negative  Pink

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. gram staining procedure

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

Crystal Gram’s (Primary stain) Gram’s (Primary stain) Gram’s Crystal violet Gram’s iodine Safranin Alcohol

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 with water Gently wash

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

Answer: Gram-positive streptococcus

Answer: Gram-negative bacilli