Question

Write a one paragraph summary about Laboratory Exercise 2: Staining Bacterial Cells .The summary should include the main concepts/techniques covered that day.

Answer 1

Gram staining is a common technique that is used for staining of bacterial cells.This technique helps to differentiate two groups of bacteria based on the different constituents of their cell wall .The Gram stain technique mostly distinguishes between Gram positive and Gram negative groups as they color the cells violet and red respectively. While Gram positive bacteria stain violet as they possess a thick layer of peptidoglycan in their cell walls that helps to retain the crystal violet during decoloring process ; gram negative bacteria stain red,as they possess a thin peptidoglycan wall that fails to retain the crystal violet during the decoloring process.Cells are first stained with crystal violet dye and after that Gram's iodine solution is added so that a complex is formed between the crystal violet and iodine. This complex being a larger molecule is insoluble in water.Next,a decolorizer e.g ethyl alcohol or acetone is added to the sample that functions to dehydrate the peptidoglycan layer as a result of which the peptidoglycan layer shrinks and tightens.In Gram positive bacteria,the large crystal violet-iodine complex that is formed cannot penetrate this tight peptidoglycan layer, and therefore remains trapped in the cell whereas in case of Gram negative bacteria,its outer membrane is degraded and its thinner peptidoglycan layer is not able to retain the crystal violet-iodine complex and thus it loses the violet color.After that ,when a counterstain that is water soluble e.g safranin, is added to the sample,the gram negative cells stain red and safranin being lighter than crystal violet, it fails to disrupt the violet/purple coloration in Gram positive cells. Thus Gram positive cells are stained violet while Gram negative cells are stained red.