Question

it becomes easier to see small details as the magnification increases but the bacteria in capsules still seem difficult to see compared to the cheek and onion. Explain why this occurs. (think structure of capsule)

Answer 1

Encapsulated bacteria are difficult to be visible under microscope as the capsules do not allow most of the stains to penetrate through their highly compact structure.

Capsule is the outermost layer around the cell wall of many bacteria, made mostly of poly saccharides. The structure of capsule is highly compact, well organized and not easily washed off. As they are non-ionic in nature, most of the acidic and basic dyes fail to adhere them. So, bacteria with capsules are often stained with Negative staining techniques. By this method, the background is stained using dark, acidic dyes such as India ink, whereas the bacteria are stained with a basic dye. So, the bacterial cell appears in the colour of basic dye and the capsule will be visible as a colourless halo against the coloured background.