Gram-positive
Gram-positive
Gram-positive (pronounced: /ɡræm ˈpɒzɪtɪv/) refers to a group of bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories.
Etymology
The term "Gram-positive" is named after the Danish bacteriologist Hans Christian Gram, who developed the Gram stain. Gram-positive bacteria retain the crystal violet dye used in the test, and thus are stained violet, while Gram-negative bacteria do not, and are thus stained red.
Characteristics
Gram-positive bacteria are characterized by having a thick peptidoglycan cell wall, and an absence of the outer membrane found in Gram-negative bacteria. This structural feature is responsible for the retention of the crystal violet dye during the Gram stain procedure.
Related Terms
- Gram-negative: Bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation.
- Peptidoglycan: A polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of most bacteria, forming the cell wall.
- Gram stain: A method of staining bacterial cells while viewing them under a microscope to determine if they are Gram-positive or Gram-negative.
See Also
External links
- Medical encyclopedia article on Gram-positive
- Wikipedia's article - Gram-positive
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