Gram Stain of Gram-negative Bacteria E. coli @1000xTM

Gram-negative Bacterial Cell Wall - P2


Photographic guides to differential stains 
now available!
1. Gram
2. Acid-fast
3. Endopsore

Gram-negative Escherichia coli @ 1000xTM
This differential staining not only colors the bacteria, but the specific stain reaction distinguishes between two meaningful categories of bacteria based on the differences in their cell wall structure.

​Page last updated: 11/2015
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Prokaryotic Cell, Mariana Ruiz
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Gram Negative Bacteria as Pathogens
Many Gram-negative bacteria are pathogens; bacteria that can cause disease. This pathogenicity is typically associated with lipopolysaccharide (LPS) endotoxins in Gram-negative cell walls, and other Gram-negative virulence factors such as the fimbriae, which help bacteria adhere to cells they can infect, and an additional layer called a capsule, which helps them stick and hide from the host' immune system.

Sources & Resources
  • Bauman, R. (2014) Microbiology with Diseases by Taxonomy 4th ed.
  • Park Talaro, K. (2008) Foundations in Microbiology.
  • Gram Stain Bite Sized Tutorial: This is an extremely useful tutorial that shows, step-by-step, the Gram-staining procedure and the appearance of Gram+ and Gram- bacterial cells.

After the Gram stain procedure, Gram+ cells appear purple; their thick layers of peptidoglycan having retained the primary stain, crystal violet. Because Gram negative cells have a very thin layer of peptidoglycan layer, these cells do not retain the purple primary stain. At the end of the Gram staining procedure, Gram-negative cells retain the secondary stain, safanin, and appear pink.

Gram Stain Procedure