Some bacteria fixed on a glass slide were stained with cryst

Some bacteria fixed on a glass slide were stained with crystal violet, soaked with iodine and then washed with alcohol. Which of the following bacteria can be seen on the slide examined under a light microscope?

A. Escherichia coli, a Gram negative bacillus.

B. Neisseria gonorrhoeae, a Gram negative coccus.

C. Treponema pallidum, a very thin spirochete.

D. Mycoplasma pneumoniae, a bacterium without cell wall.

E. None of the above

Solution

Answer

E. None of the above

Because only Gram Positive bacteria are visualized under light microscope by using Grams Stain.

Escherichia Coli, Neisseria gonorrhoeae and Treponema pallidum are gram nagative, hence they can not be seen by using this stain.

Mycoplasma pneumoniae is a very small bacteria. In addition it also lacks cell wall, therefore can not be stained by Grams Stain