BiologyMedical

Difference Between Gram Positive Bacteria and Gram Negative Bacteria

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Main Difference

We know bacteria as an invisible creature that can make us sick, but very lesser we know that bacteria can also useful for living organism apart from being harmful. Mainly, there are seven types of bacteria, which are divided by the two major types of bacteria; gram positive bacteria and gram negative bacteria. The Danish scientist Hans Christian Gram came up with the idea of differentiating it between both these types of bacteria by the structural difference of their cell walls and their stain ability when they are stained with Gram stain. The scientist mentioned above devised a lab method named ‘Gram Staining’ to differentiate it between both these types of bacteria. In this method, the gram stain, which is usually the weak alkaline solution of crystal violet is stained with bacteria. The bacteria, which retains the crystal violet dye is identified as Gram Positive Bacteria, whereas the bacteria, which does not retain the violet dye is identified as the gram-negative bacteria. Later, when the negative gram bacteria is stained with safranin or fuchsin in the experiment, it gives red or pink color.

Comparison Chart

Gram Positive BacteriaGram Negative Bacteria
Gram StainingAfter undergoing the ‘Gram Staining’ process, the bacteria, which retains the crystal violet dye is identified as Gram Positive Bacteria.After undergoing the ‘Gram Staining’ process, the bacteria, which does not retain the violet dye is identified as the gram-negative bacteria.
PeptidoglycanThickerThinner
Cell WallThicker and smooth.Thinner and wavy.
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What is Gram Positive Bacteria?

It is one of the main type of bacteria that is identified by a method devised by the Danish scientist Hans Christian Gram. The lab method, which distinguishes this type of bacteria from the other famous type of bacteria is named after the scientist himself, ‘Gram Staining’ method. Bacteria is the prokaryotic organism that is composed of the special layer called peptidoglycan; this layer is either thick or thin in size. In Gram-positive bacteria, peptidoglycan layer is thick, and that is why when this type of bacteria is stained with the Gram stain it retains the crystal violet dye. The cell wall of the gram-positive bacteria is thick as like the peptidoglycan layer and is smoother as compared to the wall of the other famous type of bacteria. In the experiment of Gram’s staining, the bacteria cells are washed with alcohol (de-staining solution) after they are treated with the iodine solution. Upon this, the bacteria which retains the crystal violet dye is identified as the gram-positive bacteria.

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What is Gram Negative Bacteria?

It is one of the main type of bacteria that is also identified after it undergoes a standard lab experiment called ‘Gram Staining.’ One of the most notable differences between this type of bacteria and other types of bacteria is that it doesn’t retain the violet dye when they are washed with the alcohol. In the experiment of Gram’s staining, the bacteria cells are washed with alcohol (de-staining solution) after they are treated with the iodine solution. Upon this, the bacteria which do not retain the crystal violet dye is identified as the gram-negative bacteria. Later, when the negative gram bacteria is stained with safranin or fuchsin in the experiment, it gives red or pink color. The reason negative bacteria loses the color is that it has the thin layer of the peptidoglycan, and upon staining it couldn’t retain the violet dye.

Gram Positive Bacteria vs. Gram Negative Bacteria

  • After undergoing the ‘Gram Staining’ process, the bacteria, which retains the crystal violet dye is identified as Gram Positive Bacteria, whereas the bacteria, which does not retain the violet dye is identified as the gram-negative
  • In Gram-positive bacteria, peptidoglycan layer is thick as compared to the peptidoglycan layer in gram-negative
  • The cell wall of the gram-positive bacteria is thicker as compared to the cell wall of the gram-negative
  • The cell wall of gram positive bacteria is smooth, whereas the cell wall of gram-negative bacteria is wavy.
  • When the negative gram bacteria is stained with safranin or fuchsin in the experiment, it gives red or pink color.
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Comparison Video

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Janet White

Janet White is a writer and blogger for Difference Wiki since 2015. She has a master's degree in science and medical journalism from Boston University. Apart from work, she enjoys exercising, reading, and spending time with her friends and family. Connect with her on Twitter @Janet__White

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