Gram-positive Bacterial Cell Wall - P2


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

Gram Positive Bacteria, Staph. epidermidis @1000xTM
Gram-positive Staphylococcus epidermidis @ 1000xTM+
The differential Gram stain 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 Positive Bacteria
Gram+ bacteria are extremely diverse. Some are pathogens, others normal flora that is beneficial to our body. There are important groups that live in the soil and are vital to the cycling of nutrients, and yet other types of Gram+ bacteria that are used to manufacture antibiotics.

Sources & Resources
  • Bauman, R. (2014) Microbiology with Diseases by Taxonomy, 4th ed.
  • 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 Gram staining, 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, safranin, and appear pink.