Why is heat or surfactant not required during the application of the counterstain in acid-fast staining?

Answer 1

Just a guess, but no heat is needed to help the stain penetrate the waxy wall because these are not acid fast bacteria-no thick waxy walls. Those have already been stained. The heat prior helped the stain penetrate the walls.

Answer 2

It is because acid fast bacteria lack a cell wall. A cell wall makes it difficult for a stain to penetrate the bacteria that possess it. Hence, heat or a surfactant is required to make it permeable to the stain by either softening the wall (in the case of heat) much the same way it is easier to add colour to candle wax when it is molten than when it is solid, or making the cell wall water soluble (in the case of surfactants) in the same way detergent makes grease water soluble, which is required because stains are water soluble. Both methods increase the permeability of the cell wall to a stain. However, in acid fast bacteria, this is not required because the cell wall is absent so the stain readily penetrates the bacteria. --- -Answer supplied by Salu Kenneth A., Olabisi Onabanjo University, Nigeria

Answer 3

Heat or surfactant is not required during the application of the counterstain in acid-fast staining because the counterstain (usually methylene blue or basic fuchsin) is not affected by the acid-alcohol decolorization step. This allows the counterstain to penetrate bacterial cells that have lost the primary stain (carbolfuchsin) and stain them, without the need for additional heat or surfactant to aid in penetration.

Answer 4

Only nonacid-fast cells undergo decolorization and these cells may now absorb the counter stain and take on a blue color.