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  • ICAR and TNAU E-Course Summarized

    Summarized Notes
  • Gram staining was discovered by Gram in year –

    Question: Gram staining was discovered by Gram in year –

    Options:

    1762
    1932
    1884
    1890

    ✅Explanation:
    Hans Christian Gram developed the Gram staining technique in 1884. This technique remains a fundamental tool in microbiology for differentiating bacteria based on their cell wall structure, aiding in identification and diagnosis.

    🔑Key Points:
    -The scientist H.C. Gram differentiated the bacteria on the basis of staining

    ✏️Gram Staining of bacteria is performed as below:
    -Firstly, the bacteria are stained with Crystal Violet then with KI solution.
    -After the staining, bacteria are washed with Acetone or Ethyl alcohol. 
    -Due to washing, some bacteria lose their stain while the other retains them.
    -Bacteria that retain stain (violet or purple) are called Gram + and bacteria that decolourise or lose the stain are called Gram – bacteria.
    -Gram-negative bacteria are counterstained with Saffranine. 
    -Gram-positive bacteria have a thick cell wall made up of peptidoglycan. The crystal violet enters the cell and forms a complex with iodine.
    -This complex gives a purple stain to the cell wall.
    -Too large to pass through this thick wall, this crystal violet-iodine complex is not removed by the alcohol rinse (washing), and the stain remains violet.
    -Now, to counter the stain red-colored safranin dye is applied, but it gets masked by the crystal violet-iodine complex.
    -Gram-negative have a thin cell wall made of peptidoglycan, located between the cell membrane and the outer membrane.
    -The crystal violet-iodine complex can easily pass through this thin cell wall and hence it gets removed with the alcohol washing.
    -The counterstain safranin stains the cell pink or red.
    Thus, it is clear gram staining identifies bacteria on the basis of the cell wall.​ 🛑Additional Information
    -Cytoplasm: It is the jelly-like material present inside the cell, that is the main arena of all cellular activities.
    -Cytoplasmic granules: These are small condensed cellular materials that appear as spots. These are also called inclusion bodies. They perform the function of nutrient storage in bacteria

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