Frequent question: Why is it that India ink stains the background instead of the capsule?

Why is India ink also called negative staining?

India Ink or Nigrosin is an acidic stain. This means that the stain readily gives up a hydrogen ion (proton) and the chromophore of the dye becomes negatively charged. Since the surface of most bacterial cells is negatively charged, the cell surface repels the stain.

What is the purpose of using a background stain in capsule staining?

Capsule is an layer around the bacteria cell which gives bacteria the protection and pathogenicity. Staining such an layer is difficult with the normal stains so it is necessary to stain the background and the cell itself which makes the capsule appear colourless.

Which stain is used for capsule?

Bacterial capsules are non-ionic, so neither acidic nor basic stains will adhere to their surfaces. Therefore, the best way to visualize them is to stain the background using an acidic stain and to stain the cell itself using a basic stain. We use India ink and Gram crystal violet.

Is a Gram stain a negative stain?

A Gram stain is colored purple. When the stain combines with bacteria in a sample, the bacteria will either stay purple or turn pink or red. If the bacteria stays purple, they are Gram-positive. If the bacteria turns pink or red, they are Gram-negative.

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Is India ink safe?

Use India Ink

Do not use just any old ink for your stick and poke. Ink, like the ink from your pen, is not sterile and can be highly toxic. A non-toxic ink, like India ink, would be your best bet. It’s natural, carbon-based, and less likely to cause infection.

What is the purpose of the simple stain procedure?

Simple staining can be used for all types of bacterial cells to give contrast to the other- wise colorless cell in order to determine cell morphology, size, and cell grouping. This technique is simple because only one dye is used and direct because the actual cell is stained.