Question

+ Organism Staining method (ZN ork) Color Cellular morphology and arrangement Acid-fast reaction (+/-) Staphylococcus epidermidis Mycobacterium smegmatis (Ctrl)

Answer 1

Ziehl-Neelsen staining is a testing carried out to check for the acid-fast bacteria. In acid-fast bacteria, a high concentration of lipid called mycolic acid is present in the cell wall which restricts acid alcohol entering into the cell.

In ZN staining, initially carbol fuchsin (primary dye) is added to the cells, all bacteria including acid-fast bacteria picks up the dye. Later a decolorizer, acid alcohol is added which removes dye from the non- acid fast bacteria whereas acid-fast bacteria doesn't allow acid alcohol inside the cell and retains primary dye. Later secondary dye, methylene blue (counter dye) is added to the cell, only non acid- fast bacteria picks up the dye hence look blue.

So with this staining procedure, acid-fast bacteria looks red (carbol fuchsin) and non acid fast bacteria look blue ( methylene blue).

In above case, Mycobacterium sp. contain mycolic acid in their cell wall and hence are acid-fast bacteria whereas Staphylococcus sp. donot contain mycolic acid and hence are non acid fast bacteria.

Organism	Staining method	Cellular morphology and arrangment	Color	Acid-fast
Staphylococcus epidermidis	ZN	Cocci (circular) and in clusters	Blue	Negative
Mycobacterium smegmatis	ZN	Bacilli (Rod) and individual	Red	Positive