2.3: Exercise #8 - Differential Staining- Gram Staining

OER - BIOL 2420 Laboratory Manual · LibreTexts

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    Exercise Outcomes:

    Course Laboratory Learning Outcomes

    THECB - ACGM Lab Learning Outcome #1 Use and comply with laboratory safety rules, procedures, and universal precautions

    THECB - ACGM Lab Learning Outcome #2 Demonstrate proficient use of a compound light microscope.

    THECB - ACGM Lab Learning Outcome #3 Describe and prepare widely used stains and wet mounts and discuss their significance in identification of microorganisms.

    THECB - ACGM Lab Learning Outcome #4 Perform basic microbiology procedures using aseptic techniques for transfer, isolation, and observation of commonly encountered, clinically significant bacteria.

    Laboratory Exercise Learning Outcomes
    1. Define differential staining.
    2. Define primary stain, secondary stain (counter-stain), and mordant.
    3. List and describe the differential stains that will be performed in the laboratory this semester
    4. Describe the purpose of the Gram stain.
    5. Describe the protocol for the Gram stain; properly identify all reagents.
    6. Perform the Gram stain correctly in the laboratory setting.
    7. Differentiate between Gram-positive and Gram-negative reactions.
    8. Describe the importance of the Gram stain in disease detection and diagnosis.
    9. Describe the Gram stain reaction for species studied in the laboratory.
    10. Interpret possible causes for errors in the Gram stain procedure.

    Materials Needed:

    • Bunsen burner
    • Microscope slides (one for each bacterial sample)
    • Staining tray (Containing stains (crystal violet, Gram's iodine, safranin), decolorizer (acetone, alcohol or acetone/alcohol mixture), stain rack, and DI water)
    • China marker
    • Lens cleaner
    • Lens paper
    • Kim wipes
    • Broth cultures of bacteria
    • Test tube rack
    • Inoculating loop
    • Microscope

    In this laboratory exercise, you will be performing the first of two types of differential stains. Differential staining procedures are staining procedures that allow an observer to differentiate or separate cells based on staining differences. These staining techniques allow the observer to examine cell shape, cell size, and cell arrangement like simple stains; but unlike simple stains allow the observer to obtain additional information about the sample. Differential stains allow for the detection of structural variations between two types of cells or the identification of parts of the same organism. Differential staining techniques also differ from simple stain, in that they make use of two stains rather than just one stain.

    This page titled 2.3: Exercise #8 - Differential Staining- Gram Staining was last modified on Sat, 25 Jul 2026 03:42:51 GMT and is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by Sherry Smith.