Gram negative

Definition

Gram-negative bacteria are a group of bacteria that do not retain the crystal violet stain used in Gram staining. They have a thin peptidoglycan layer and an outer membrane containing lipopolysaccharides.

5 Must Know Facts For Your Next Test

1. Gram-negative bacteria have an outer membrane that contains lipopolysaccharides, which can be toxic to humans.
2. They appear pink or red after Gram staining due to the counterstain safranin.
3. The outer membrane of Gram-negative bacteria contributes to their resistance to certain antibiotics.
4. Examples include Escherichia coli, Salmonella, and Neisseria gonorrhoeae.
5. Their cell wall structure includes a thin peptidoglycan layer located between the inner cytoplasmic cell membrane and the bacterial outer membrane.

Review Questions

• What color do Gram-negative bacteria appear after Gram staining?
• Why are Gram-negative bacteria often more resistant to antibiotics compared to Gram-positive bacteria?
• Name two examples of Gram-negative bacteria.

Related terms

Gram-positive bacteria: Bacteria that retain the crystal violet stain in Gram staining, appearing purple due to a thick peptidoglycan layer.

Peptidoglycan: A polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of most bacteria.

Lipopolysaccharide (LPS): A large molecule consisting of lipid and polysaccharide found in the outer membrane of Gram-negative bacteria, contributing to their structural integrity and toxicity.