Question

Describe the color of both gram-positive and gram-negative cells after each of the four steps in the gram staining method (not including rinsing with water). Why does alcohol easily decolonize gram negative bacteria, but not those that are gram-negative? How are the results of a gram stain important in prescribing a treatment for a bacterial information?

Answer 1

Gram staining:-

Procedure:

1. Primary staining with a dye such as gentian violet.

2. application of dilute solution of iodine.

3. Decolourisation with an organic solvent such as ethanol.

4. Counterstaining with a dye of contrasting colour such as safranine or neutral red.

- After four steps in the gram staining method the colour of gram-positive bacteria will be violet and that of gram-negative bacteria will be red.

- Gram-positive bacteria are those that resist decolourisation and retain the primary stain, appearing violet. Gram-negative bacteria are decolourised by organic solvents and therefore take the counterstain , appearing red.

2. Alcohol easily decolourisises gram-negative bacteria, but not those that are gram-positive due to following reasons:-

- The peptidoglyacan of gram-positive bacteria is thicker than gram negative bacteria thus able to retain the dye-iodine complex.

- Gram-positive cells have a more acidic protoplasm which may account for their retaining the basic primary dye strongly than Gram-negative bacteria.

- The high lipid content of Gram-negative bacteria makes them permeable to secondary dye after decolourisation with organic solvent like alcohol.

3. Based on the gram staining report physician can know the type of bacteria whether it is Gram-positive or gram-negative bacteria. According to the type of bacteria physician can prescribe desired antibiotics.

So before prescribing any antibiotics one must know the type of bacteria for which he is prescribing antibiotics.

Specific antibiotics can be given.

- Hope you got your answer.