What is the difference between gram positive and gram negative bacteria?

In Gram staining, an unknown bacteria is differentiated into one of two groups of bacteria- those with a thick cell wall high in peptidoglycan and those with a thin cell wall with a negligible amount of peptidoglycan. Two stains are applied, and whichever one adheres to the cell will determine which kind of bacterium is being observed. The first or primary stain is crystal violet. The second or secondary stain is saffranin (though fuschin is sometimes used).

Gram (+) bacteria have a thick cell wall high in peptidoglycan and lipids. Gram (-) bacteria have a thinner cell wall composed mainly of techoic acids. Thus, the primary stain (crystal violet) adheres to the peptidoglycan during the first phase of staining. Gram's Iodine is applied and acts as a mordant which in the case of Gram (+) bacteria will tighten the binding of the stain to the fine meshwork of peptidoglycan those bacteria.

Next the slide is rinsed with ethcanol alcohol. In Gram (+) bacteria, this binded stain will be carried away when rinsed with ethanol alcohol. The stain, now properly binded, does not leave the cell wall and is displayed. However if the cell is Gram (-), th

In Gram (+) bacteria, peptidoglycan is dissolved by ethanol alcohol, removing both the peptidoglycan and the primary stain (crystal violet), allowing the positively charged secondary saffranin stain to infiltrate inside the cell wall where it is attracted to the overall negatively-charged environment inside that cell. When the cell is counterstained with saffranin, the inside of the cell is colored pink or reddish.

Hence, the Gram (+) bacteria appear violet due to their retention of the primary crystal violet staining, and Gram (-) bacteria appear pink or reddish due to their loss of the primary stain and the infliltration into their cell bodies of the secondary saffranin staining.

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