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Cell wall theory: Cell wall of Gram positive bacteria are 40 times thicker than those of Gram negative cells, hence they are thought to help retain the dye-iodine complex.
Lipid CONTENT Theory: Cell envelope of Gram negative bacteria contains an ADDITIONAL membrane (outer membrane). hence CONTAINING more lipids than Gram positive bacteria. Acetone or alcohol dissolves the lipid thus forming large PORES in Gram negative bacteria through which the dye-iodine complex leaks out. Alcohol/acetone dehydrates Gram positive bacteria shrinking the cell wall and the closing the pores.
Magnesium Ribonucleate Theory: A compound of magnesium ribonucleate and basic protein CONCENTRATED at the cell membrane helps Gram positive bacteria retain the primary dye. Gram negative bacteria do not possess this substance.
Cytoplasmic pH Theory: The cytoplasm of Gram positive bacteria are said to be more acidic (2) than those of Gram negative ones (3). Hence the dye is said to bind with more affinity to Gram positive cells.

Cell wall theory: Cell wall of Gram positive bacteria are 40 times thicker than those of Gram negative cells, hence they are thought to help retain the dye-iodine complex.
Lipid Content Theory: Cell envelope of Gram negative bacteria contains an additional membrane (outer membrane). hence containing more lipids than Gram positive bacteria. Acetone or alcohol dissolves the lipid thus forming large pores in Gram negative bacteria through which the dye-iodine complex leaks out. Alcohol/acetone dehydrates Gram positive bacteria shrinking the cell wall and the closing the pores.
Magnesium Ribonucleate Theory: A compound of magnesium ribonucleate and basic protein concentrated at the cell membrane helps Gram positive bacteria retain the primary dye. Gram negative bacteria do not possess this substance.
Cytoplasmic pH Theory: The cytoplasm of Gram positive bacteria are said to be more acidic (2) than those of Gram negative ones (3). Hence the dye is said to bind with more affinity to Gram positive cells.

Hans CHRISTIAN Gram invented this stain in 1884. The original formulation was Aniline GENTIAN VIOLET. Lugol’s iodine, absolute ALCOHOL and Bismark BROWN.

Hans Christian Gram invented this stain in 1884. The original formulation was Aniline Gentian violet. Lugol’s iodine, absolute alcohol and Bismark brown.

LoetTler’s methylene blue SOLUTION treated with Potassium HYDROXIDE turns into Polychrome methylene blue after prolonged STORAGE with shaking. Used in McFadyean’s reaction for Bacillus anthracis in blood FILMS and demonstration of metachromatic granules of CORYNEBACTERIUM diphtheriae.

LoetTler’s methylene blue solution treated with Potassium hydroxide turns into Polychrome methylene blue after prolonged storage with shaking. Used in McFadyean’s reaction for Bacillus anthracis in blood films and demonstration of metachromatic granules of Corynebacterium diphtheriae.

Stains are classified based on the pH of their chromophore (color bearing ion) into acidic, basic and neutral. Acidic dyes have anionic chromophore

eg.. sodium+ eosinate-. Basic dyes have cationic chromophore eg.. metFiylene blue+ chloride-. Acidic dyes combine more strongly with cytoplasmic components of bacteria, especially the nucleus that is basic in NATURE. Neutral dyes have both acidic and basic component that nullity each other.

They are Romanowsky’s STAIN and are USED in STAINING parasitic forms. Stains can be either natural (eg: carmine and hematoxylin) or coal-tar derivatives /aniline stains (eg: methylene blue. CRYSTAL violet). Supravital (cells removed from the body) and intravital (cells still a part of the body).

Stains are classified based on the pH of their chromophore (color bearing ion) into acidic, basic and neutral. Acidic dyes have anionic chromophore

eg.. sodium+ eosinate-. Basic dyes have cationic chromophore eg.. metFiylene blue+ chloride-. Acidic dyes combine more strongly with cytoplasmic components of bacteria, especially the nucleus that is basic in nature. Neutral dyes have both acidic and basic component that nullity each other.

They are Romanowsky’s stain and are used in staining parasitic forms. Stains can be either natural (eg: carmine and hematoxylin) or coal-tar derivatives /aniline stains (eg: methylene blue. crystal violet). Supravital (cells removed from the body) and intravital (cells still a part of the body).

• Simple stain: where only one stain is used and all bacteria are stained similarly. Eg: F1ethylene blue, dilute carbol fuchsin
• DIFFERENTIAL staining: where different bacteria stain DIFFERENTLY to a common staining technique depending on their physiological properties. Eg: Gram’s stain and Acid fast staining
• Special stain: where STRUCTURES of bacteria like SPORES. granules. capsule etc are demonstrated. Eg: silver impregnation technique for demonstration of spirochetes. Feulgen stain for demonstration of nucleus. Sudan black stain for demonstration of lipid vacuoles. Ryu’s stain for demonstration of flagella. Albert’s stain for demonstration of metachromatic granules.
• Negative staining: where the background is stained with an ACIDIC dye such as India ink or Nigrosin. Used for demonstration of capsules.