The principle of Leifson stain lies in using a colloidal precipitate formed by tannic acid and a dye to thicken bacterial flagella, making them visible under a light microscope.
Here's a breakdown of the principle:
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Flagella are thin: Bacterial flagella are extremely thin structures, often below the resolution limit of standard light microscopy. This makes them difficult to observe directly.
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Precipitate Formation: The Leifson stain utilizes tannic acid and a dye (often pararosaniline or basic fuchsin) to create a colloidal precipitate. This precipitate is a suspension of tiny particles within a liquid.
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Adsorption and Thickening: This colloidal precipitate is adsorbed onto the flagella. As the precipitate particles attach, they effectively increase the diameter of the flagella. The flagella become thicker, making them more readily visible under the microscope.
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Staining: Simultaneously, the dye within the colloidal precipitate stains the thickened flagella, providing color contrast that further enhances their visibility against the background.
In essence, the Leifson stain "coats" and stains the flagella, building them up to a size where they can be clearly visualized using standard light microscopy.
