How does beating the bacterial smear during a ZN stain promo

How does beating the bacterial smear during a ZN stain promote entry of carbolfuchsin into the acid-fast cell wall? Are acid-fast negative cells stained by carbolfuchsin? If so, how can this be a differential stain? Why do you suppose the acid fast stain is not as widely used as the Gram stain? When is it more useful than the Gram stain?

Solution

1. the cell wall of acid fast bacteria contain high concentration of lipids making them waxy, hydrophobic and impermeable to routine stains such as Gram stain.The main lipid is mycolic acid .By heating the lipids melt, which helps in the penentration of the stains inside the cell.

2. the acid fast stain is a differential stain that distinguishes organisms with waxy cell walls that can reisist decolorization with acid alcohol.

carbol fuchsin is the primary stain in this procedure and it contains phenol which helps solubilize the cell wall.Heat is also applied during staining to increase stain penentration.All types of cell will take up primary stain.The cells are then decolorized with acid alcohol which decolorizes all cells except the acid fast ones.Methlene blue is the applied to counterstain any cells which have not been decolorized.In the end, acid fast cells will be reddish pink,and nonacid fast cells will be blue.

3.Acid fastness is a characteristic that is shared by a few organisms,which have a thick layer of mycolic acid .Gram stain are virtually applicable to any kind of bacteria, seperating them into two groups,gram positive and gram negative .But acid fast staining can only be done for the identification of infections by Mycobacterium, Nocardia and Cyanobacteria.