Question

Questions 1 Often, upon doing a negative pom doing a negative stain of unencapsulated Gram-negative cells, a small halo will be seen around the cells. Why is this the case? What external structure of Gram-negative cell will acude the negative stain? 2 What are the functions of a bacterial capsule? 3 Does a species produce a capsule under all conditions of cultivation? Explain. 4 Why is the size of a bacterium more accurate for a negative stain than a direct staining method 5 What should be the effect on the staining if the sample was heat-fixed before staining

Answer 1

1.when negative stain of an encapsulated Gram negative cells is done a small halo that appears is the Lipopolysaccharide Layer that does not take up the negative stain hence appears like a halo.

2. The functions of the Bacterial Caspule are

i. To provide virulence : it enhances the capacity of the bacteria to produce disease

ii. Protects the bacteria from phagocytosis, toxic metabolites, detergents, bacterial viruses, clearance from the immune system,camouflages the bacteria from the immune system by mimicking the host tissues

iii. Helps the bacteria to adhere/attach to surfaces

iv. Promotes concentration of nutrients at the bacterial cell surface because of its polyanionic nature

v. Certain capsules have water which prevents the bacteria from drying

3. A capsule is not produced during all stages of cultivation, as the bacterial specie may not need the virulence factor during all stages .

4. Negative staining techniques doesnt involve the step of heat fixation which thus prevents the distortion of the cell and cell organelles thereby yielding more accurate cell size as compared to direct staining wherein heat fixation is involved.

5. Heat Fixation is not included in the protocol of Negative staining as, heat fixation may lead to distortion of cell and its organells especially the capsule.