The three types of hemolysis are alpha, beta, and gamma hemolysis.
Hemolysis refers to the breakdown of red blood cells. When bacteria are grown on blood agar plates, their hemolytic properties can be observed based on the appearance of the agar around the colonies. This is a key characteristic used in bacterial identification.
Here's a breakdown of each type:
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Alpha-hemolysis (α-hemolysis): This is partial hemolysis. The bacteria partially break down the hemoglobin in red blood cells, resulting in a greenish or brownish discoloration around the colonies on the blood agar. This discoloration is due to the reduction of hemoglobin to methemoglobin. An example of a bacteria exhibiting alpha-hemolysis is Streptococcus pneumoniae.
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Beta-hemolysis (β-hemolysis): This is complete hemolysis. The bacteria completely lyse the red blood cells, creating a clear, colorless zone around the colonies on the blood agar. This indicates that all the hemoglobin in the red blood cells has been broken down. An example of a bacteria exhibiting beta-hemolysis is Streptococcus pyogenes.
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Gamma-hemolysis (γ-hemolysis): This is no hemolysis. The bacteria do not cause any breakdown of red blood cells, and there is no change in the appearance of the blood agar around the colonies. The area around the colonies remains red. While called "gamma-hemolysis," it is technically the absence of hemolysis. Enterococcus faecalis (formerly Streptococcus faecalis) is often considered to exhibit gamma-hemolysis.
| Type of Hemolysis | Description | Appearance on Blood Agar | Example Bacteria |
|---|---|---|---|
| Alpha (α) | Partial hemolysis; incomplete breakdown of hemoglobin. | Greenish or brownish zone around colonies. | Streptococcus pneumoniae |
| Beta (β) | Complete hemolysis; complete breakdown of hemoglobin. | Clear, colorless zone around colonies. | Streptococcus pyogenes |
| Gamma (γ) | No hemolysis; no breakdown of hemoglobin. | No change; blood agar remains red around colonies. | Enterococcus faecalis |
In summary, the three types of hemolysis (alpha, beta, and gamma) are visually distinguished by the changes they cause to blood agar, allowing for preliminary identification of bacterial species.
