Difference Between Alpha And Beta Hemolysis

Hemolysis is the breakdown of red blood cells. Hemolysis is used in the empirical identification of microorganisms based on the ability of bacterial colonies grown on agar plates to break down red blood cells in the culture. When the organism has been grown on blood agar plates, it can be classified with regard to whether or not it has caused hemolysis in the red blood cells (RBCs) incorporated in the medium. This is of particular importance in the classification of streptococcal species. A substance that causes hemolysis is a hemolysin. While a blood agar plate may contain varying concentrations of RBCs and may use blood from a variety of animals, clinical results are most often reported on 5-10% sheep blood agar plates (SBAP).

 Types of hemolysis include:

• Alpha hemolysis
• Beta hemolysis
• Gamma hemolysis

Alpha Hemolysis

Alpha hemolysis (α-hemolysis) is present if there is a greenish darkening of the agar under the colonies. Streptococcus pneumoniae and Streptococcus viridans display alpha hemolysis. This is sometimes called green hemolysis because of the color change in the agar. Other synonymous terms are incomplete hemolysis and partial hemolysis. Alpha hemolysis is generally caused by peroxides produced by the bacterium.

What You Need To Know About 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.
• Alpha hemolysis is also known as partial hemolysis or green hemolysis.
• Alpha hemolysis is a type of partial hemolysis of red blood cells.
• Alpha hemolysis is caused by hydrogen peroxide produced by the bacterium.
• Hydrogen peroxide oxidizes hemoglobin (red) to methemoglobin (green).
• Red blood cells remain intact in alpha hemolysis.
• Alpha hemolysis produces greenish black zones.
• The width of the zone is 1-2 mm in alpha hemolysis.
• Streptococcus pneumonia and Streptococcus viridans undergo alpha hemolysis.
• The species that cause alpha hemolysis are found in the oral cavity.

Beta Hemolysis

Beta hemolysis (β–hemolysis) is caused by a complete lysis of the red cells in the media. The area around and under the colonies are lightened and transparent. Streptococcus pyogenes, or Group A beta-hemolytic Strep, displays beta hemolysis. Hemolytic tests are also used to differentiate Staphylococcus aureus, which displays beta-hemolysis, from S. epidermidis, a non-hemolytic, commensal species. Beta hemolysis is sometimes called complete hemolysis. Beta hemolysis is caused by hemolysins.

• Some weakly beta hemolytic species will cause intense beta hemolysis when grown together with a strain of Staphylococcus. This is called the CAMP test¹. Streptococcus agalactiae displays this property. Clostridium perfringens can be identified presumptively with this test.
• If an organism does not cause hemolysis, it is said to display gamma hemolysis (γ-hemolysis): the agar under and around the colony is unchanged (this is also called non-hemolytic). Enterococcus faecalis (formerly called Group D Strep) displays gamma hemolysis.

What You Need To Know About 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.
• Beta hemolysis is also known as complete hemolysis.
• Beta hemolysis is a type of complete hemolysis of red blood cells that surround the colony.
• Beta hemolysis is caused by the toxic by-products that destroy red blood cells.
• Beta hemolysis is involved in the complete rupture of red blood cells.
• Red blood cells are broken down in beta hemolysis.
• Beta hemolysis produces clear zones.
• The width of the zone is 2-4 mm in beta hemolysis.
• Streptococcus pyogenes undergoes beta hemolysis.
• The species that cause beta hemolysis are found in the throat.

Difference Between Alpha And Beta Hemolysis In Tabular Form