6 What could happen if too little nigrosin is used in the pr

6. What could happen if too little nigrosin is used in the preparation of a negative stain?

Solution

Preparation and staining of a bacteria smear using a negative stain:

1). Obtain the sample from the source and mix it in a drop of India ink or nigrosin on a glass slide.

2). Spread the mixture on the side and form a smear.

3). Allow the slide to dry naturally, without heating.

4). After drying, the organisms appear clearly against the dark background (slide should not be washed).

Nigrosin is used to colour the background but the bacteria remain colourless, means to contrast the background and bacteria. As both the nigrosin and bacterial membrane are negatively charged, they undergo repulsion. To achieve better contrast, sufficient nigrosin is necessary. If less nigrosin is added, contrasting will be difficult.