Gram-positive

Definition

Gram-positive bacteria are a group of bacteria that retain the crystal violet stain used in the Gram staining procedure, appearing purple under a microscope. They have a thick peptidoglycan layer in their cell walls and lack an outer membrane.

5 Must Know Facts For Your Next Test

1. Gram-positive bacteria have a thicker peptidoglycan layer compared to Gram-negative bacteria.
2. They appear purple after Gram staining due to retention of the crystal violet dye.
3. Examples include Staphylococcus and Streptococcus species.
4. Some Gram-positive bacteria can form endospores, which are resistant to harsh conditions.
5. They generally lack an outer membrane, which is present in Gram-negative bacteria.

Review Questions

• What color do Gram-positive bacteria appear after Gram staining?
• Name two examples of Gram-positive bacteria.
• How does the peptidoglycan layer of Gram-positive bacteria differ from that of Gram-negative bacteria?

Related terms

Gram-negative:

Bacteria that do not retain the crystal violet stain and appear red or pink due to a thinner peptidoglycan layer and an outer membrane.

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

Endospore: A dormant, tough, and non-reproductive structure produced by certain bacteria that allows them to survive extreme conditions.