10 Questions
Who developed the Gram staining method in 1884?
Hans Christian Gram
What is the function of the mordant in the Gram staining procedure?
To form a crystal violet-iodine complex
What is the characteristic of the cell wall of Gram-positive bacteria?
Thick layer of peptidoglycan and low lipid content
What is the purpose of the decolorization step in the Gram staining procedure?
To distinguish gram-positive from gram-negative cells
What is the purpose of the counterstain in the Gram staining procedure?
To stain the decolorized gram-negative cells
What is the effect of the organic solvent on gram-negative bacteria during the decolorization step?
It extracts the blue dye complex from gram-negative bacteria
What is the final color of gram-positive bacteria after the Gram staining procedure?
Blue/purple
What is the purpose of heating the clinical material during the fixation step?
To fix the clinical material to the microscope slide
Why is the quality of the smear important in the Gram staining procedure?
It affects the Gram Stain results
What is the purpose of washing the slide with tap water during the Gram staining procedure?
To remove excess crystal violet
Study Notes
Gram Staining Method
- Developed by Danish physician Hans Christian Gram in 1884
- Still the cornerstone of bacterial identification and taxonomic division
Differential Staining Procedure
- Separates most bacteria into two groups based on cell wall composition
- Two groups: Gram-positive and Gram-negative bacteria
Gram-Positive Bacteria
- Thick layer of peptidoglycan (90% of cell wall)
- Stains purple
Gram-Negative Bacteria
- Thin layer of peptidoglycan (10% of cell wall) and high lipid content
- Stains red/pink
Gram Staining Procedure
- Fixation of clinical materials to the microscope slide
- Application of primary stain (crystal violet) that stains all cells blue/purple
- Application of mordant (iodine solution) to form a crystal violet-iodine complex
- Decolorization step that distinguishes Gram-positive from Gram-negative cells
- Application of counterstain (safranin) that stains decolorized Gram-negative cells red/pink
Materials Needed
- Microscopic slides
- Inoculating loop
- Distilled water
- Absorbent paper
- Oil-immersion lens
- Microscope
- Gram staining reagents
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