Question

Which of the following stain is used to observe bacteria under the microscope
A. Malachite green
B. Methylene blue
C. Crystal Violet
D. None of these

Answer 1

Hint: The crystal violet increases the contrast of both gram-negative and gram-positive bacteria making them appear purple.

Step by step answer:The stain is taken up by the bacterial cell wall due to the presence of peptidoglycan.
The Gram-positive bacteria are stained with crystal violet and appear purple under the microscope.
 The Gram-negative bacteria are stained with safranin and appear pink.
The microscope is a very important tool in microbiology, but there are limitations when it comes to using one to observe cells in general and bacterial cells in particular. Two of the most important concerns are resolution and contrast.
Resolution is a limitation that we can’t do much about since most bacterial cells are already near the resolution limit of most light microscopes.
Contrast, however, can be improved by either using a different type of optical system, such as phase contrast or a differential interference contrast microscope, or by staining the cells (or the background) with a chromogenic dye that not only adds contrast, but gives them colour as well. There are many different stains and staining procedures used in microbiology. Some involve a single stain and just a few steps, while others use multiple stains and a more complicated procedure. Before the staining procedure, the cells have to be mounted (smeared) and fixed onto a glass slide. A bacterial smear is simply that—a small amount of culture spread in a very thin film on the surface of the slide.
Probably the most important feature made obvious when stain bacterial cells are their cellular morphology (not to be confused with colonial morphology, which is the appearance of bacterial colonies on an agar plate). Often bacteria create specific arrangements of cells, which form as a result of binary fission by the bacteria as they reproduce. Arrangements are particularly obvious with non-motile bacteria because the cells tend to stay together after the fission process is complete.

Hence, the correct option is C

Note: Because many differential staining methods require several steps and take a long time to complete, we will not be performing all of the differential staining methods discussed above. Pre-stained slides will be used to visualize bacterial capsules, metachromatic granules, and acid-fast bacilli.