Capsule Stain- Principle, Procedure and Result Interpretation


Capsule stain is a special staining technique that allows the visualization of the capsule, a slimy layer of polysaccharides or polypeptides that surrounds some bacterial cells. The capsule is an important virulence factor for many pathogenic bacteria, as it protects them from phagocytosis by host immune cells, enhances their adherence to surfaces, and prevents dehydration. Therefore, capsule stain can be used to identify and differentiate encapsulated bacteria from non-encapsulated ones.

However, capsule stain is not a simple procedure, as the capsule is usually colorless and does not take up most of the conventional stains. Moreover, the capsule is easily distorted or destroyed by heat-fixing or harsh chemicals. Therefore, capsule stain requires a careful and delicate technique that preserves the integrity of the capsule and contrasts it with the cell body and the background.

In this article, we will explain the principle, procedure and result interpretation of one of the most commonly used methods for capsule stain: the Anthony capsule stain. This method involves the use of crystal violet as the primary stain and copper sulfate as the decolorizing agent. By following this method, you will be able to observe the capsule as a clear halo around the purple cell against a blue background. We will also discuss the importance of capsule stain in microbiology and medicine.