Question

microbiology questions:

What is the purpose of the negative stain?

why is size and shape more accurate in the negative stain than other stains?

what property of nigrosin makes it suitable chemical for the negative stain?

Answer 1

Negative staining, is the procedure in which background is stained and cells remain untouched.

1.The main purpose of Negative staining is to study the morphological shape, size and arrangement of the bacteria cells that is difficult to stain. eg: Spirilla. It can also be used to stain cells that are too delicate to be heat-fixed.

2.Negative staining can be useful for accurately determining cell dimensions. Because of absence of heat fixing , no shrinkage of the cell occurs and size determinations are more accurate than those determined on fixed material.

3.

Nigrocin is an acidic, anionic dye is mixed with a cell sample. The dye readily gives up a hydrogen ion and becomes negatively charged. Since the surface of most bacterial cells is negatively charged, the cell surface repels the stain and background readily change the color and not the cells, causing the cells to stand out.