Properties of dyes Why dyes color microbial cells? Because dyes absorb radiation energy in visible region of electromagnetic spectrum i.e., “light”(wave length 400-650). And absorption is anything outside this range it is colorless. E.g., acid fuschin absorbs blue green and transmit red. General methods of staining
1. Direct staining Is the process by which microorganisms are stained with simple dyes. E.g., methylene blue
2. Indirect staining – is the process which needs mordants.
A mordant is the substance which, when taken up by the microbial cells helps make dye in return, serving as a link or bridge to make the staining recline possible.
It combines with a dye to form a colored “lake”, which in turn combines with the microbial cell to form a “ cell-mordant-dye- complex”. It is an integral part of the staining reaction itself, without which no staining could possibly occur. E.g., iodine.
A mordant may be applied before the stain or it may be included as part of the staining technique, or it may be added to the dye solution itself. An accentuator, on the other hand is not essential to the chemical union of the microbial cells and the dye. It does not participate in the staining reaction, but merely accelerate or hasten the speed of the