Capsule stain is a type of differential stain which uses acidic and basic dyes to stain background & bacterial cells respectively so that presence of capsule is easily visualized. Capsule is synthesized in the cytoplasm and secreted to the outside of the cell where it surrounds the bacterium.
What stains are used for capsule staining?
The capsule stain employs an acidic stain and a basic stain to detect capsule production.
Procedure of Capsule Staining
Place a small drop of a negative stain (India Ink, Congo Red, Nigrosin, or Eosin) on the slide. Using sterile technique, add a loopful of bacterial culture to slide, smearing it in the dye.
What type of staining is used for capsules and why?
Bacterial capsules are non-ionic, so neither acidic nor basic stains will adhere to their surfaces. Therefore, the best way to visualize them is to stain the background using an acidic stain and to stain the cell itself using a basic stain. We use India ink and Gram crystal violet.
What color is a capsule stain?
In a capsule stained microscope image, the bacterial cells will typically be stained purple, and the background of the slide should be darkly stained. Against this dark background, the capsules of the bacteria, if present, will appear as a clear halo around the cells.
Is capsule stain a differential stain?
Capsule stain is a type of differential stain which involves the use of two stains; primary stain and the counterstain. Here, it’s worth noting that for most part, capsules are non-ionic. As a result, acidic and basic stains will often fail to adhere on to them.
Are capsules negatively stained?
We need to utilize negative staining techniques to view the outline of the capsule. Negative stains are repelled by the negatively charged bacterial cells preventing the cells from taking up the stain. Therefore, in negative staining the background (rather than the microorganism) is stained.
Why don’t you heat fix a capsule stain?
Most bacterial capsules are composed of polysaccharide however some genera produce polypeptide capsules. Capsular material is very moist (slimy) and any heating will cause it to shrink – it is for this reason that we will not heat fix the slide before staining.
Why are capsule stains not rinsed with water?
How it works: Capsules are highly ordered polymers of sugars and proteins that surround some bacterial cells, and can be easily dislodged by heat or water. Accordingly, capsule stains are not heat-fixed, and water is never used to rinse.
How is the capsule stain used in clinical microbiology?
The purpose of the capsule stain is to reveal the presence of the bacterial capsule. The water-soluble capsule of some bacterial cells is often difficult to see by standard simple staining procedures or after the Gram stain.
How do I make a capsule stain?
Procedure of Capsule Stain
Prepare thin smears of bacterial culture on a microscope slide.Allow the smear to only air-dry. Apply 1% crystal violet and allow it to remain on the slide for 2 minutes.With the slide over the proper waste container provided, gently wash off the crystal violet with 20% copper sulfate.
What are the two different methods of capsule staining?
The first is a wet-mount method using india ink; the capsule is visualized as a refractile zone surrounding a cell. The second is a direct-staining dry-mount method that precipitates copper sulfate and leaves the capsule as a pale blue zone. Both methods are easily performed within approximately 5 min.
What is Fimbriae microbiology?
Fimbriae are long filamentous polymeric protein structures located at the surface of bacterial cells. They enable the bacteria to bind to specific receptor structures and thereby to colonise specific surfaces.
Why is malachite green used in endospore staining?
The presence of endospores in a bacterial culture can be detected by staining with malachite green. Because the endospore coat is so tough, steam is used to enable dye penetration. After washing, only the endospores will retain the primary stain Malachite green.
What does an endospore look like?
Endospores: Endospores are bright green. Vegetative Cells: Vegetative cells are brownish red to pink. Spores may be located in the middle of the cell, at the end of the cell, or between the end and middle of the cell. Spore shape may also be of diagnostic use.
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