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Complete 6 pages APA formatted article: Selective And Differential Media For Identifying Microorganisms.
Complete 6 pages APA formatted article: Selective And Differential Media For Identifying Microorganisms. Gram-positive bacteria which retain the crystal violet and hence appear deep violet in color and Gram-negative bacteria which lose the crystal violet, are counterstained by the safranin and hence appear red in color.
The most plausible explanations for this phenomenon are associated with the structure and composition of the cell wall. Difference between the thickness of cell walls of Gram-negative and Gram-positive bacteria is imperative.
The cell walls of Gram-negative bacteria are generally thinner than those of Gram-positive bacteria. Gram-negative bacteria contain a higher percentage of lipid than do Gram-positive bacteria. Experimental evidence suggests that during staining of Gram-negative bacteria, the alcohol treatment extracts the lipid, which results in increased porosity or permeability of the cell wall. Thus the CV-I complex can be extracted and Gram-negative organism is decolorized. These cells subsequently take on the color of the safranin counterstain. Since walls of Gram-negative bacteria have a smaller amount of peptidoglycan, which is less extensively cross-linked than that in the wall of Gram-positive bacteria, therefore the pores of the cell wall of Gram-negative bacteria remain large even after ethanol treatment to allow alcohol to extract CV-I complex.
The cell walls of Gram-positive bacteria because of their different composition (lower lipid content), become dehydrated during treatment with alcohol. The pore size decreases, permeability is reduced and the CV-I complex cannot be extracted. Therefore, these cells remain purple-violet. Alcohol causes a diminution in the diameter of the pores in the cell-wall peptidoglycan (Web. Gram Staining).
Staphylococcus spp. occur most commonly as irregular clusters of spherical cells and Streptococcus spp. are cocci that divide in a single plane forming chains. Both these organisms are Gram-positive.
