The Uses Of Differential Stain

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Erica Stevens June 2, 2015 Gram Stain Laboratory Report

Purpose:
To understand how the use of differential stains can help us identify cell morphology. Also to identify the presence of two different bacteria in our mixed sample by identifying differences in color, shape and grouping of eubacteria.

Theory and Background:
Gram stain is the most important and “commonly used differential stain in microbiology” (1). Developed by Hans Christian Gram in 1884, while searching for a way to visualize bacteria in lung tissue of people who had died from pneumonia. Gram used crystal violet as the primary stain, iodine as the mordant followed by treatment with ethanol as a
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The cell membrane is a selectively permeable barrier composed of a phospholipid bilayer and proteins. This layer of the cellular envelope, protects the cell from bursting under external osmotic pressure and for communication between cells. The cell wall is found on the outer surface of the cellular envelope, and it is here that the composition of the cell differs (4). In gram-positive cells, the cell membrane is separated from the cell wall by a thin periplasmic space. The periplasmic space is an area for storage of enzymes secreted by the cell membrane and synthesis of peptidoglycan (3). The cell wall is composed of peptidoglycans; many long chains of glycans linked together by peptides creating a permeable mesh-like surface. In gram-positive cells the layers of peptidoglycans is very thick (20-80nm) and it protects the cell from bursting from internal pressure (3,4). The cell wall also contains polysaccharides (teichoic acid and lipoteichoic acid) that are embedded in the peptidoglycan structure. These structures assist in maintenance of the cell wall, cell division and pathogenic functions of the cell (3). Gram-negative cells have a larger periplasmic space that separates the cell membrane from the cell wall. This periplasmic membrane is the site for metabolic reactions (3). The cell wall in gram-negative
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