Gram-negative bacteria

Definition

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

5 Must Know Facts For Your Next Test

1. Gram-negative bacteria are often more resistant to antibiotics due to their outer membrane.
2. The outer membrane of gram-negative bacteria contains endotoxins, which can cause severe reactions in humans.
3. Escherichia coli and Pseudomonas aeruginosa are common examples of gram-negative bacteria.
4. In a Gram stain test, gram-negative bacteria appear red or pink after counterstaining with safranin.
5. Gram-negative bacteria play significant roles in human microbiomes and environmental ecosystems.

Review Questions

• Why are gram-negative bacteria typically more resistant to antibiotics?
• What color do gram-negative bacteria appear after a Gram stain test?
• Name two examples of gram-negative bacteria.

Related terms

Gram-positive Bacteria: Bacteria that retain the crystal violet stain and appear purple in a Gram stain test due to a thick peptidoglycan layer.

Peptidoglycan:

A polymer that forms a protective structural layer outside the plasma membrane of most bacteria.

Endotoxin:

Toxins located within the bacterial cell wall, specifically found in the outer membrane of gram-negative bacteria, which can trigger strong immune responses.