3.4: Summary of Common Bacterial Staining Techniques
- Page ID
- 15967
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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