Capsule Stains
Some bacteria are surrounded by layers of material that lie external to the rigid cell wall, these are the capsule and slime layer (Figure). Anatomically they can be divided into the following three categories, (i) macrocapsules which are demonstrable by light microscope and are at least 0.2 μm thick. They firmly remain attached to the cell and have definite-external surface, (ii) microcapsules are capsular layers less than 0.2 μm in thickness and they are detected immunologically and (iii) slime layers, which may part freely from cells as they are formed and hence have little anatomical significance.
Microorganisms which produce capsules often form a layer of slime similar, if not, identical in composition to the capsular material.
