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3.4: Summary of Common Bacterial Staining Techniques

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    Simple Stains:

    Crystal Violet, Methylene Blue, Safranin

    • Used to provide color to otherwise transparent bacterial cells
    • Can be used to determine cell size, morphology and arrangement

    Gram Stain

    Primary stain – crystal violet

    Mordant – iodine; decolorizer- 95% Ethanol

    Counterstain – Safranin

    • Common differential stain
    • Gram reaction (positive or negative) reflects cell wall properties
    • Also used to determine cell size, morphology and arrangement

    Acid-Fast Stain

    Primary stain – Carbol fuchsin

    Decolorizer – acid alcohol

    Counterstain – Methylene blue

    • A differential stain used to detect bacteria with mycolic acid cell walls (genera Mycobacterium and Nocardia)
    • Developed to detect the bacterial species that causes tuberculosis
    • Acid-fast organisms resist decolorization with acid-alcohol

    Endospore Stain

    Primary stain - Malachite green

    Counterstain - safranin

    • Endospores resist staining with basic stains
    • Endospores stain with malachite green; vegetative cells stain with safranin

    Capsule Stain (Negative staining)

    Uses an acidic stain: (Congo red or Nigrosin) and a basic stain: (crystal violet or safranin)

    • Negative stains are neither heat-fixed nor rinsed
    • The background of the slide is stained by acidic stains (capsule remains unstained)
    • The cells within the capsule are stained with Basic stains
    • Examples of encapsulated cells: Bacillus anthracis, Streptococcus pneumoniae, and Klebsiella pneumonia

    Flagella Stain

    Silver nitrate

    • Used to see bacterial flagella that are too slender to be seen with other staining techniques
    • Silver nitrate makes flagella appear larger than they are
    • Can be used to determine arrangement of flagella for identification.
      • Ex: Proteus vulgaris has peritrichous flagella

    Spirochete stain

    Silver nitrate

    • Used to visualize slender spirochetes like Treponema pallidum

    3.4: Summary of Common Bacterial Staining Techniques is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by Joan Petersen & Susan McLaughlin.

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