Bacterial cell wall

There are two different types of cell wall in bacteria, called Gram-positive and Gram-negative. The names originate from the reaction of cells to the Gram stain. Gram-positive bacteria become violet because they retain crystal violet stain with their thick layer of peptidoglycans (from 15 to 80 nm). The Gram-negative bacteria (as they do not retain crystal violet stain but retain fuchsin) appear pink. They have a very thin layer of peptidoglycans and an outer membrane containing lipopolysaccharides. They also have some proteins in this outer membrane.

Streptococcus sp.

Gram positive

Escherichia coli

Gram negative

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Bacterial cell wall