Hans Christian Gram a Danish scientist developed a technique known as Gram staining in 1884; it is used to stain bacteria. The solution used to stain the bacteria, Gram stain, is a weak alkaline solution of gentian violet or crystal violet. The process of Gram staining has allowed scientist to classify bacteria into two categories: gram positive or gram negative. When a bacterium retains the color of the Gram stain it is considered Gram positive bacteria.
When gram stain test are conducted the bacteria is washed with a decolorizing solution after they have been dyed with a crystal violet. A counter-stain is then added like safranin of fuchsine after washing. If the bacteria is gram negative the bacteria becomes stained red or pink. If the bacteria is gram positive the bacteria retains the color of the crystal violet dye. The reason is because the structure of the cell wall on gram positive bacteria is different than the cell wall on gram negative bacteria.
Gram Positive Bacteria
Gram positive bacteria will react by retaining the stains color when they are washed typically with absolute alcohol and water. They have a thick multilayered peptidoglycan layer. Teichoic acid is present in many of the bacteria and periplasmic space is absent. There is no outer membrane and virtually no lipopolysaccharide content. In Gram positive bacteria the resistance to physical disruption, inhibition by basic dyes, susceptibility to anionic detergents, and the resistance to dying and sodium azide, all remain high. Furthermore the cell wall is characterized as being 100 single layered a its Armstrong thickness is approximately 100 to 120, with a low lipid content which makes the Murein content 70 to 80% higher. These types of bacteria are more susceptible to antibiotics.
Gram Negative Bacteria
Gram negative bacteria will react by decolorizing; it accepts counter stain. When washed typically with absolute alcohol and water gram negative bacteria will not retain the Gram stain. They have a thin single-layered peptidoglycan layer. Teichoic acid is absent and periplasmic space is present. There is an outer membrane and a high lipopolysaccharide content. In Gram positive bacteria the resistance to physical disruption, inhibition by basic dyes, susceptibility to anionic detergents, resistance to sodium azide, and the resistance to dying all remain low. Furthermore the cell wall is characterized as being two layer and the Armstrong thickness is approximately 70 to 120, with a high lipid content which makes the Murein content 10 to 20% lower. These types of bacteria are more resistant to antibiotics.
Conclusion
The main difference between gram positive bacteria and gram negative bacteria is that gram positive bacteria do not have the outer cell membrane that gram negative bacteria does. The gram positive in turn has a high peptiodoflcan content which causes it to retain the Gram stain color.