Main Difference – Alpha vs Beta Hemolysis
Streptococcus is a type of gram-positive bacteria that occur as clusters or short chains. It is a type of facultative anaerobe that grows under oxygen-free environments. It also grows in mucous membranes of the animal body as commensals. But under certain conditions, it causes infections in red blood cells. Hemolysis is the break down of red blood cells. Hemolysin is the substance that causes hemolysis. Three types of hemolysis may occur as a result of Streptococcus infection: alpha hemolysis, beta hemolysis, and gamma hemolysis. The main difference between alpha and beta hemolysis is that alpha hemolysis is involved in partial hemolysis associated with the reduction of hemoglobin in red blood cells whereas beta hemolysis is involved in the complete hemolysis of red blood cells that surround the colony.
Key Areas Covered
1. What is Alpha Hemolysis
– Definition, Process, Examples
2. What is Beta Hemolysis
– Definition, Process, Examples
3. What are the Similarities Between Alpha and Beta Hemolysis
– Outline of Common Features
4. What is the Difference Between Alpha and Beta Hemolysis
– Comparison of Key Differences
Key Terms: Alpha Hemolysis, Beta Hemolysis, Blood Agar, Gram-Positive Bacteria, Hemolysin, Hemolysis, Red Blood Cells, Streptococcus
What is Alpha Hemolysis
Alpha hemolysis refers to the partial hemolysis of red blood cells shown by the greenish discoloration surrounding the bacterial colony in the blood agar. It is caused by several Streptococcus species such as Streptococcus pneumonia and Streptococcus viridans. Alpha hemolysis is a type of partial hemolysis in which the iron molecules in the hemoglobin are oxidized by hydrogen peroxide produced by the bacteria. This gives the greenish color to the surroundings of the bacterial colony as hemoglobin is converted into methemoglobin. Alpha hemolysis is not a complete rupture of red blood cells; the red blood cells remain intact during the infection. Gamma hemolysis is another type of hemolysis; here, no damage to the red blood cells occurs by the bacteria. It occurs in Enterococcus faecalis, Neisseria meningitidis, and Moraxella catarrhalis. Alpha and gamma hemolysis are shown in figure 1.
Figure 1: Alpha (green) and Gamma (Red) Hemolysis
However, the prolonged incubation allows the formation of clear areas in alpha hemolysis. However, green or brown shades remain in the medium. As alpha hemolysis occurs by Streptococcus pneumonia, it can be used as a diagnostic feature during the identification of the bacterial strain.
What is Beta Hemolysis
Beta hemolysis refers to the complete breakdown of red blood cells, demonstrated by a clear zone surrounding the bacterial colony in the blood agar. It is involved in the true or complete lysis of red blood cells. The toxic by-products of bacteria cause the complete breakdown of red blood cells. Streptococcus pyogenes produces a hemolysin called Streptolysin O, which is only active in low oxygen conditions. Anaerobic pockets can be produced on the agar plate by stabbing an inoculating loop into the agar vertically, after streaking the plate. Some Streptococcus pyogenes species produce an oxygen-stable hemolysin called Streptolysin S. Beta hemolysis is shown in figure 2.
Figure 2: Beta Hemolysis
Some beta hemolysis reactions are very subtle. These weak hemolysis reactions occur in Streptococcus agalactiae or Listeria monocytogenes.
Similarities Between Alpha and Beta Hemolysis
- Alpha and beta hemolysis are two types of hemolysis caused by Streptococcus
- Both alpha and beta hemolysis can be demonstrated on blood agar.
Difference Between Alpha and Beta Hemolysis
Definition
Alpha Hemolysis: Alpha hemolysis refers to the greenish discoloration and partial hemolysis of the red blood cells immediately surrounding colonies of some streptococci on blood agar plates.
Beta Hemolysis: Beta hemolysis refers to the complete breakdown of red blood cells demonstrated by a clear zone surrounding the bacterial colony in the blood agar.
Alternative Names
Alpha Hemolysis: Alpha hemolysis is also known as partial hemolysis or green hemolysis.
Beta Hemolysis: Beta hemolysis is also known as complete hemolysis.
Type of Hemolysis
Alpha Hemolysis: Alpha hemolysis is a type of partial hemolysis of red blood cells.
Beta Hemolysis: Beta hemolysis is a type of complete hemolysis of red blood cells that surround the colony.
Hemolysins
Alpha Hemolysis: Alpha hemolysis is caused by hydrogen peroxide produced by the bacterium.
Beta Hemolysis: Beta hemolysis is caused by the toxic by-products that destroy red blood cells.
Process
Alpha Hemolysis: Hydrogen peroxide oxidizes hemoglobin (red) to methemoglobin (green).
Beta Hemolysis: Beta hemolysis is involved in the complete rupture of red blood cells.
Rupture of Red Blood Cells
Alpha Hemolysis: Red blood cells remain intact in alpha hemolysis.
Beta Hemolysis: Red blood cells are broken down in beta hemolysis.
Change
Alpha Hemolysis: Alpha hemolysis produces greenish black zones.
Beta Hemolysis: Beta hemolysis produces clear zones.
Width of the Zone
Alpha Hemolysis: The width of the zone is 1-2 mm in alpha hemolysis.
Beta Hemolysis: The width of the zone is 2-4 mm in beta hemolysis.
Type of Streptococcus
Alpha Hemolysis: Streptococcus pneumonia and Streptococcus viridans undergo alpha hemolysis.
Beta Hemolysis: Streptococcus pyogenes undergoes beta hemolysis.
Location
Alpha Hemolysis: The species that cause alpha hemolysis are found in the oral cavity.
Beta Hemolysis: The species that cause beta hemolysis are found in the throat.
Conclusion
Alpha and beta hemolysis are two types of hemolysis that occur by the infection of different Streptococcus species. Both alpha and beta hemolysis can be demonstrated using blood agar plates. Alpha hemolysis is a type of partial hemolysis that produces green color zones surrounding the bacterial colony in the blood agar. However, beta hemolysis is a type of complete hemolysis that produces clear zones surrounding the bacterial colony. Therefore, the main difference between alpha and beta hemolysis is the degree of hemolysis.
Reference:
1. “BLOOD AGAR PLATES AND HEMOLYSIS PROTOCOLS.” American Society for Microbiology, Available here.
Image Courtesy:
1. “Alpha and gamma hemolysis on blood agar with a scale bar” By HansN. – Own work, CC BY-SA 3.0) via Commons Wikimedia
2. “Beta hemolysis on blood agar” By HansN. – Own work (CC BY-SA 3.0) via Commons Wikimedia
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