2 Laboratory Report 13 Studen Date 18 Capsular Staining A. Results 1. Draw cells

Question

2 Laboratory Report 13 Studen Date 18 Capsular Staining A. Results 1. Draw cells that display a capsule from your stained slide of Klebsiella pneumoniae. Explain how the cap sule is visualized without the use of dyes that adhere to a capsule. Klebsiella pneumoniae (capsular stain) B. Short-Answer Questions 1. What are two functions of the capsule or glycocalyx in bacterial cells? 2. What biological molecules can make up the bacterial capsule or glycocalyx? 3. What function does the capsule have for Streptococcus mutans? 4. A student heat-fixes his smear intended for capsule staining. What result might the student expect? 103

Explanation / Answer

13. A. Please examine the slide under oil-immersion objective and then sketch your observation.

In Klebsiella pneumoniae capsulated diplococci will appear as clear zones between the cell wall and dark background.

B. 1. Capsules can serve a number of functions, depending on the bacterial species.

i. They provide protection against temporary drying by binding water molecules,

ii. They block attachment of bacteriophages.

iii. They may be antiphagocytic; i,e, they inhibit the engulfment of pathogenic bacteria by white blood cells and thus contribute to invasive or infective ability (virulence).

iv. They promote attachment of bacteria to surfaces.

v. If capsules are composed of composed of compounds having an electrical charge, such as sugar-uronic acids, they may promote the stability of bacterial suspension by preventing the cells from aggregating and settling out, because cells bearing similarly charged surfaces tend to repel one another.

2. Capsules are composed of single kind of polysaccharides called homopolysaccharides. They are synthesized outside the cell from disaccharides by exocellular enzymes. The synthesis of glucan (a polymer of glucose) from sucrose by Streptococcus mutans is an example.

Other capsules are composed of several kinds of sugars and are termed heteropolysaccharides. These are synthesized from sugars and precursors that are activated (energized) within the cell, attached to a lipid carrier molecule, transported across the cytoplasmic membrane, and polymerised outside the cell. Klebsiella pneumoniae is an example.

A few capsules are composed of polypeptides. Example: Bacillus anthracis composed entirely of a polymer of glutamic acid.

3. In Streptococcus mutans, capsule promote the attachment of bacteria to surfaces. This bacteriumi associated with producing dental caries, firmly adheres to the smooth surfaces of teeth because of its secreton of a water0insoluble capsular glucan.

4. Heating results in shrinkage which may create a clear zone around the cell that is an artifact and that can be mistaken for the capsule. Hence never heat fix the bacterial smear in capsule staining.

12. A. Examine the silde under oil -immersion objective and write the diagram after your observation.

The streptococci, yeast and spirochetes in the sample can be distinguished in negative staining based on size and shape of the organisms.

Strptococci - spherical in shape and arranged in chains (3 or more).

Yeast - size is bigger than cocci, oval in shape sometimes occur in budding stage (can be mistaken as streptococci).

Spirochetes - spirilla shape

B. 1. In negative staining, the background but nit the bacterium is stained by the use of an acidic stain which carries a negative charge on its surface and is repelled by the bacteria that too carry a negative charge on their surface.

2. India Ink or aqueous nigrosin is used for negative stain.

3. Cells are going to be distorted when heat fixing is done.Hence heat-fing is usually avoided when dimensions of cells are determined.

4. In negative staining, external bacterial cell strucure like capsule can be demonstrated.

Capsule is a mucilaginous substance forming a viscous coat around the cell.

Related Questions

Navigate

• Browse (All)
• Browse 2
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.