Final answer:
Negative staining, commonly using India ink or nigrosin, is the primary technique used to stain capsuled bacteria, revealing the capsule as a clear halo around the cell.
Step-by-step explanation:
The staining technique used for capsuled bacteria is known as negative staining.
This method is particularly effective because the capsule does not absorb most basic dyes, allowing it to remain unstained and appear as a halo around the borders of the cell.
Among the commonly used negative stains are India ink and nigrosin, which stain the background but not the capsule itself.
In some cases, a combination of positive and negative staining can be employed, where the positive stain colors the body of the cell, and the negative stain colors the surroundings, leaving the capsule clear.
For example, a technician observing capsuled bacteria might use India ink to create a contrasting background, making the transparent capsule visible as a clear halo around the bacteria.
This is vital in diagnostics as the presence or absence of a capsule can be a significant indicator of the microbe's virulence.