23.03.2023 - 00:25

Explain the steps of the staining method for acid-fast stain.


Explain the steps of the staining method for acid-fast stain.

Answers (1)
  • Eros
    April 9, 2023 в 20:37

    The acid-fast stain is a laboratory technique used to differentiate acid-fast bacteria from non-acid-fast bacteria. This staining method is commonly used to identify mycobacteria, such as Mycobacterium tuberculosis, which are responsible for causing tuberculosis.

    The acid-fast staining method involves several steps as follows:

    1. Preparation of the smear: A thin smear of the bacterial sample is prepared on a clean glass slide and allowed to air dry.

    2. Fixation: The smear is fixed onto the slide by heat fixation, which involves passing the slide through a flame a few \times.

    3. Primary staining: The smear is then covered with a solution of carbolfuchsin, a red dye that is lipid-soluble and can penetrate the bacterial cell wall. The slide is heated over a steam bath for several minutes to allow the dye to penetrate the bacterial cells.

    4. Decolorization: After staining, the slide is washed with acid-alcohol, which removes the carbolfuchsin dye from non-acid-fast bacteria but not from acid-fast bacteria.

    5. Counterstaining: The smear is then counterstained with a contrasting dye, usually methylene blue, which stains non-acid-fast bacteria blue, while the acid-fast bacteria remain red.

    6. Microscopic examination: The stained smear is then examined under a microscope for the presence of acid-fast bacteria. Acid-fast bacteria will appear as red, rod-shaped structures, while non-acid-fast bacteria will appear blue.

    In conclusion, the acid-fast staining method involves a series of steps that allow for the differentiation of acid-fast bacteria from non-acid-fast bacteria. The primary stain, carbolfuchsin, penetrates the bacterial cell wall of both acid-fast and non-acid-fast bacteria, but the decolorization step removes the dye from non-acid-fast bacteria. The counterstain, methylene blue, is used to stain the non-acid-fast bacteria, making them visible under the microscope. Acid-fast bacteria remain red after the counterstain, allowing for their identification.

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