How to Do a Gram Stain
Test for Gram+ & Gram- Bacteria Identification
Peptidoglycan is a huge polymer of interlocking chains of NAG and NAM polysaccharide monomers connected by interpeptide bridges.
Bacterial Cell Wall: Peptidoglycan Structure
This rigid structure of peptidoglycan gives the bacterial cell shape, surrounds the plasma membrane and provides prokaryotes with protection from their environment.
Article Summary: Gram staining involves the application of a series of dyes that leaves some bacteria purple (Gram +) and others pink (Gram -). Here's how the Gram stain works.
Gram Stain for Identifying Gram +/- Bacteria
Page last updated: 11/2015
How to Prepare a Bacterial Smear
for Gram Staining
In the 1800’s, Hans Christian Gram, a Danish bacteriologist, developed a technique for staining bacteria that is still widely used today.
The Gram stain protocol involves the application of a series of dyes that results in some bacteria staining purple and others pink.
Bacteria that stain purple are considered Gram-positive, and those that stain pink, Gram-negative. The specific stain reaction of a bacterium results from the structure of the bacterial cell wall.
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A smear is a sample of bacteria suspended in a small amount of water on a slide. That sample is then dried using heat. The heat kills the bacteria and attaches the sample to the slide so that it does not easily wash away.
Gram Stain Procedure Video!