Question

Are all bacteria either Gram positive or Gram negative? If not, what is an example of a different type of bacteria?

Answer 1

Most of the bacteria can be classified as either gram-positive or gram-negative based on their capacity to retain the gram stain. Gram-positive bacteria are those which possess a thick peptidoglycan layer which traps the gram stain so the bacteria appear purple. Bacteria which do not possess this thick peptidoglycan layer can not hold the gram stain. They are counterstained by safranine and appear as red cells when viewed after the staining procedure is complete.

However, in nature, there are some bacteria which don't respond to gram stain and known as gram intermediate bacteria. One example is Mycobacterium tuberculosis. Some bacteria are known as gram variables as some cells are stained purple and some cells are stained pink when gram staining procedure is employed.