What is the purpose of capsule in bacteria?
What is the function of capsule in bacteria? Capsules can protect a bacterial cell from ingestion and destruction by white blood cells (phagocytosis). While the exact mechanism for escaping phagocytosis is unclear, it may occur because capsules make bacterial surface components more slippery, helping the bacterium to escape engulfment by ...
How do capsules protect bacteria?
They contribute to virulence in the following ways:
- By protecting bacteria from phagocytosis.
- By preventing complement mediated cell lysis.
- Capsules protect bacteria from dessication and action of lysozymes.
- Biofilm formation (more appropriately it is the slime layer).
Do all bacteria have a capsule?
The remainder of the bacteria only are often capsuled. All bacteria have a slime layer on their surfaces and when visible under the microscope, they are reffered to as capsule. In a sense, if bacteria are in it's natural habitat in the animal tissue, the capsule is visible under microscope.
What is the function of bacterial capsule *?
The intermediate layer performs different functions related to its composition:
- Avoid drying: the sugars forming this layer are hydrophilic molecules, they retain and absorb water protecting the cell from dehydration;
- Promotes cell-cell and cell-substrate adhesion;
- Reserve: from polysaccharides are obtained by reduction of sugar monomers used as an energy source in case of need;
What is the capsule of a bacterial cell?
The bacterial capsule is a large structure common to many bacteria. It is a polysaccharide layer that lies outside the cell envelope, and is thus deemed part of the outer envelope of a bacterial cell. It is a well-organized layer, not easily washed off, and it can be the cause of various diseases. The capsule—which can be found in both gram ...
What is the composition of bacterial capsules?
Composition. Most bacterial capsules are composed of polysaccharide, but some species use other materials, such as poly- D-glutamic acid in Bacillus anthracis. Because most capsules are so tightly packed, they are difficult to stain because most standard stains cannot penetrate the capsule.
What is the difference between slime and bacterial capsule?
A bacterial capsule has a semi-rigid border that follows the contour of the cell. The capsule excludes India Ink when dyed. A slime layer is a non-rigid matrix that is easily deformed and is not able to exclude India Ink . Biofilms are composed of many cells and their outer barriers. The primary functions of both capsules ...
Why are capsules important for virulence?
The capsule is considered a virulence factor because it enhances the ability of bacteria to cause disease (e.g. prevents phagocytosis ). The capsule can protect cells from engulfment by eukaryotic cells, such as macrophages. A capsule-specific antibody may be required for phagocytosis to occur. Capsules also contain water which protects the bacteria against desiccation. They also exclude bacterial viruses and most hydrophobic toxic materials such as detergents. Immunity to one capsule type does not result in immunity to the other types. Capsules also help cells adhere to surfaces. As a group where the capsule is present they are known as polysaccharide encapsulated bacteria or encapsulated bacteria.
Which bacteria synthesizes a capsule composed of polypeptide and polysaccharides?
Bacillus megaterium for example, synthesizes a capsule composed of polypeptide and polysaccharides. Bacillus anthracis. Streptococcus pyogenes synthesizes a hyaluronic acid capsule. Streptococcus pneumoniae has at least 91 different capsular serotypes. These serotypes are the basis for the pneumococcal vaccines.
What is the color of Maneval's capsule?
The background stain is the acidic stain Congo red (which changes color to bluish-grey due to the pH), and the pink stain is acid fuschin.
What is the capsule in a Gram positive?
The capsule—which can be found in both gram negative and gram-positive bacteria —is different from the second lipid membrane – bacterial outer membrane, which contains lipopolysaccharides and lipoproteins and is found only in gram-negative bacteria. When the amorphous viscid secretion (that makes up the capsule) diffuses into ...
What is a bacterial capsule?
The bacterial capsule is a large structure of many bacteria. It is a layer of polysaccharide that is found outside the cell envelope and is therefore considered part of the outer envelope of a bacterial cell. It is a well organized coat, it does not wash easily, and it can be the cause of various diseases. Bacterial Capsule.
What is the function of a capsule?
Function of capsule: Prevent the cell from desiccation and drying: capsular polysaccharide bind significant amount of water making cell resistant to drying. Protection: it protect from mechanical injury, temperature, drying etc. Attachment: capsule helps in attachment on the surface. Eg.
What is a polyvalent capsule?
Polyvalent (4 serotypes) vaccine of Neisseria meningitidis capsule. A monovalent vaccine made up of capsular material from Haemophilus influenzae. Initiation of infection: Capsules helps the organism to adhere to host cells.The capsule also facilitates and maintains bacterial colonization of biologic (e.g. teeth) and inanimate (e.g.
What is slime in bacteria?
If the capsule is too thick it is known as slime . The slime layer adheres weakly to the cell wall and can be lost with vigorous washing and subculture. Capsule composition: 98% water and 2% polysaccharide or glycoprotein / polypeptide or both. In the case of acetic acid bacteria, the capsule is composed of homopolysaccharide (hemicellulose)
What is the capsule made of?
Klebsiella pneumoniae: the capsule is made up of glucose, galactose, rhamnose, etc. In Bacillus anthracis: the capsule is made up of a polypeptide ...
What is the phenomenon of bacterial capsules?
A given bacterial species may undergo a phenomenon called S-R variation whereby the cell loses the ability to form a capsule. Some capsules are very large and absorb water; bacteria with this type of capsule (e.g., Klebsiella pneumoniae) form mucoid (M) colonies.
What happens if pathogenic bacteria lose their capsule?
If a pathogenic bacteria lose capsule (by mutation), they wont be able to cause disease (i.e. loses disease causing capacity). Saving engulfed bacteria from the action of neutrophil: Bacterial capsule prevents the direct access of lysosome contents with the bacterial cell, preventing their killing.
What Is A Bacterial Capsule?
- In most cases, the capsule is made of polysaccharides, but some of them are constructed of other materials such as Bacillus anthracis containa proteinaceous capsule which is made of poly D-glutamic...
- It is lies outside the cell envelope.
- Both gram-negative and gram-positive bacteria contain capsules. It differs from the bacterial …
- In most cases, the capsule is made of polysaccharides, but some of them are constructed of other materials such as Bacillus anthracis containa proteinaceous capsule which is made of poly D-glutamic...
- It is lies outside the cell envelope.
- Both gram-negative and gram-positive bacteria contain capsules. It differs from the bacterial outer membrane which is made of lipopolysaccharides and lipoproteins and mainly found in gram-negative...
- Capsules can be observed under a light microscope by applying negative stains or specific capsule stains on them.
Compositions of Capsules
- Most of the bacterial Capsules are made of polysaccharides but in some species it is made of other materials, For example, the capsule of Bacillus anthracisis made of poly-D-glutamic acid.
- The capsules are tightly packed layers, therefore it is difficult to stain them because most standard stains cannot penetrate the capsule. Therefore the capsule is treated with a specialized dark s...
Function of Bacterial Capsule
- Virulence Factor: Capsule is an important virulence factor for pathogenic bacteria. They are anti-phagocytic, which means they protect the bacterial cell from the phagocytosis. The negative charge...
- Prevent the cell from desiccation and drying:The bacterial capsule contains a significant amount of water which prevents the desiccation of the cell and protects the cell from benign …
- Virulence Factor: Capsule is an important virulence factor for pathogenic bacteria. They are anti-phagocytic, which means they protect the bacterial cell from the phagocytosis. The negative charge...
- Prevent the cell from desiccation and drying:The bacterial capsule contains a significant amount of water which prevents the desiccation of the cell and protects the cell from benign dry.
- Repulsion:Those bacterial cells contain the same charged capsule they repel each other.
- Protection: Capsule defends the cell from physical pressure and chemical damage.
Types of Capsule
- There are two types of capsule such as Macro-capsule 1. The thickness of the Macro-capsule is 0.2µm or more. 2. Macro-capsule are visible under a light microscope. Microcapsule 1. The thickness of the Microcapsule is 0.2µm. 2. Macro-capsule is visible under Electron microscope.
Demonstration of Capsule
- India ink staining Capsule can be visualized by using India ink staining. In this staining method, the capsule formed a clear halo around the bacterium as the ink can’t penetrate the capsule. Maneval’s capsule stain In this staining method, the capsule develops a clear halo between the pink-stained (acid fuschin) bacterium and the bluish-grey stained background (acidic stain Cong…
References
- https://www.britannica.com/science/bacteria/Capsules-and-slime-layers
- https://www.atmph.org/article.asp?issn=1755-6783;year=2015;volume=8;issue=4;spage=151;epage=153;aulast=Kandi;type=3
- http://textbookofbacteriology.net/structure_4.html
- https://microbeonline.com/bacterial-capsule-structure-and-importance-and-examples-of-cap…
- https://www.britannica.com/science/bacteria/Capsules-and-slime-layers
- https://www.atmph.org/article.asp?issn=1755-6783;year=2015;volume=8;issue=4;spage=151;epage=153;aulast=Kandi;type=3
- http://textbookofbacteriology.net/structure_4.html
- https://microbeonline.com/bacterial-capsule-structure-and-importance-and-examples-of-capsulated-bacteria/
Overview
The bacteria capsule is a large structure common to many bacteria. It is a polysaccharide layer that lies outside the cell envelope, and is thus deemed part of the outer envelope of a bacterial cell. It is a well-organized layer, not easily washed off, and it can be the cause of various diseases.
The capsule—which can be found in both gram negative and gram-positive bact…
Composition
Most bacterial capsules are composed of polysaccharide, but some species use other materials, such as poly-D-glutamic acid in Bacillus anthracis. Because most capsules are so tightly packed, they are difficult to stain because most standard stains cannot penetrate the capsule. To visualize encapsulated bacteria using a microscope, a sample is treated with a dark stain, such as India ink. The structure of the capsule prevents the stain from penetrating the cell. When viewed, bacteria…
Function
The capsule is considered a virulence factor because it enhances the ability of bacteria to cause disease (e.g. prevents phagocytosis). The capsule can protect cells from engulfment by eukaryotic cells, such as macrophages. A capsule-specific antibody may be required for phagocytosis to occur. Capsules also contain water which protects the bacteria against desiccation. They also exclude bacterial viruses and most hydrophobic toxic materials such as detergents. Im…
Diversity
The capsule is found most commonly among gram-negative bacteria:
• Escherichia coli (in some strains)
• Neisseria meningitidis
• Klebsiella pneumoniae
• Haemophilus influenzae
Demonstration of capsule
1. India ink staining: the capsule appears as a clear halo around the bacterium as the ink can't penetrate the capsule.
2. Maneval's capsule stain: the capsule appears as a clear halo between the pink-stained bacterium and the bluish-grey stained background. The background stain is the acidic stain Congo red (which changes color to bluish-grey due to the pH), and the pink stain is fuchsine.
Use in vaccination
Vaccination using capsular material is effective against some organisms (e.g., H. influenzae type b, S. pneumoniae, and N. meningitidis ). However, polysaccharides are not highly antigenic, especially in children, so many capsular vaccines contain polysaccharides conjugated with protein carriers, such as the tetanus toxoid or diphtheria toxoid. This stimulates a much more robust immune response.
See also
• Bacterial cell structure
• Quellung reaction, a method to visualize capsule under a microscope