Saturday, 26 June 2021

Capsule Staining by Maneval's Method

Capsule Staining by Maneval's Method

Bacterial cell is consisting of various structural components such as  cell wall, cell membrane, capsule, flagella etc.
Capsule is one of the important component but it is not present in all bacteria.

Accordingly bacteria are grouped as capsulated and noncapsulated. Capsule is a slimy, gummy & mucilaginous covering present around the cell wall.

Capsule is made up of 98 % water and 2 % polysaccharides and therefore it is nonionic in nature. However, capsule of some bacteria is made up of polypeptides.

Capsule protects bacterial cell from desiccation, starvation, phagocytosis and phage infection. It also give the property of virulence to the bacterial cell that mean Capsule is increased pathogenicity of an organism.

  Capsule can be demonstrated in microscope by various special staining methods like -India ink method, Anthony's method, Maneval's method & Hiss method.
Maneval's method is most commonly used method for Capsule staining.

Principle of Maneval's capsule staining

It uses the principle of negative staining for demonstration of capsule. Background is stained, cytoplasm is stained and capsule remains colourless.

Requirements

- Clean grease free slide
- Nichrome wireloop
- 24 hrs old culture of capsulated bacteria
- 1% Congo Red Solution
- Maneval's Stain

Composition of Maneval's Stain

• 1% Acid fuchsin - It stains cell cytoplasm
• 5% Phenol - It increases penetration power of stain
• 30 % FeCl3 - It is a Chemical fixative
• 20 % Acetic acid - It Changes the background from red to blue

Procedure (Steps) :

• Prepare the loop full culture smear on the slide by Nichrome wireloop, air dry but do not heat fix
• Put a drop of 1 % congo red at one end of the slide and spread it across the smear with help of another slide
• Dry the film of congo red
• Flood the smear with Maneval's stain and allow to react for 4 minutes.
• Discard the excess stain but do no wash with water.
• Dry the slide and observe under the oil immersion objective.

Microscopic Observation :

In the microscopic field you will see Blue colour background, Pink colour bacterial cell and Colourless Capsule.

Microscopic Observation of Capsule Staining by Maneval's Method

Example of capsulated bacteria :

Klebsiella spp.
Azotobacter spp.
Rhizobium spp.
Bacillus spp
Xantomonas spp.

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