Fundamentals of Microbiology

Principle

             Negative staining employs the use of an acidic stain such as lndia ink or nigrosin. The acidic stain will not penetrate the cells because of the negative charge on the surface of bacteria

Bacteria + Acidic dye      →    Repulsion of dye (Bacteria are not stained while the background is stained)

Therefore, the unstained cells are easily discernible against he coloured background.

The advantages of negative staining are that:

•    The cells are not subjected to the distorting effects of heat  and chemicals. Therefore, the natural size and shape are retained.

It is possible to observe bacteria that are difficult to stain such as some spirilli