Gram Positive

Topics: Bacteria, Staining, Gram-negative bacteria Pages: 2 (311 words) Published: October 9, 2011

1.Describe the major differences between gram positive and gram negative bacteria cell walls. The gram negative bacteria cell wall is a thin peptidoglycan layer and an outer cell membrane with a lipopolysaccharide layer. The gram positive bacteria cell wall is a single thick peptidoglycan layer. This wall forms in a mesh like formation of three layers of alternating material.

2.From the procedure that you have carried out,do you feel that the Gram positive stain is a simple procedure? No, because there are many procedure to do and more complex than simple ones and use more than one stain to differentiate cellular components.


The Gram stain procedure uses 3 different stains. These are crystal violet, Gram’s iodine, and safranin. The cells are first stained with crystal violet, then Gram’s iodine. Following a rinse in alcohol, to de-colorize the cells, the cells are then stained with safranin. The Gram stain procedure separates almost all bacteria into two large groups: the Gram-positive bacteria that stain blue and the Gram-negative bacteria that stain pink. Bacteria take up the Gram stain differently because they differ in cell wall composition. Gram-positive bacteria have a thick cell wall layer. Alcohol does not readily penetrate to decolorize the cell wall of the previously applied crystal violet stain. Gram-negative cells have a thinner cell wall through which the alcohol readily penetrates. The crystal violet is removed from these cell walls that are then stained with the safranin counterstain. Staphylococcus aureus, and Bacillus subtillis are Gram-positive and stain blue. E. coli is Gram-negative and stain pink.


Differential stains are more complex than simple ones and use more than one stain to differentiate cellular components. They are used to examine structural differences between bacterial groups or to provide contrast to different structures within the same organism.
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