Difference Between Alpha Beta and Gamma Hemolysis

The key difference between alpha beta and gamma hemolysis is that alpha hemolysis is the partial destruction of red blood cells in the blood and beta hemolysis is the complete destruction of red blood cells in the blood, while gamma hemolysis does not involve any breakdown of red blood cells.

Red blood cells contain haemoglobin molecules. Haemoglobin is an iron-containing metalloprotein and the main molecule of oxygen transportation. They are found inside the red blood cells. The destruction of red blood cells causes the release of haemoglobin from red blood cells to blood plasma. This is a process called hemolysis. A bacterial enzyme called hemolysin catalyzes the breakdown of red blood cells.  There are three types of hemolysis as alpha hemolysis, beta hemolysis and gamma hemolysis.

CONTENTS

1. Overview and Key Difference
2. What is Alpha Hemolysis
3. What is Beta Hemolysis
4. What is Gamma Hemolysis
5. Similarities Between Alpha Beta and Gamma Hemolysis
6. Side by Side Comparison – Alpha Beta vs Gamma Hemolysis in Tabular Form
7. Summary

What is Alpha Hemolysis?

Alpha hemolysis or incomplete hemolysis is the process of partial destruction of red blood cells. Alpha hemolysin enzyme catalyzes this process. It is a bacterial enzyme produced by several bacterial species such as S. pneumoniae, Streptococcus mitis, S. mutans, and S. salivarius, etc.

When these bacteria are grown in blood agar medium around their colonies, greenish colour develops due to the incomplete destruction of red blood cells. The greenish colour is due to the presence of biliverdin, and this compound is a byproduct of haemoglobin breakdown.

What is Beta Hemolysis?

Beta hemolysis or complete hemolysis is the complete destruction of red blood cells. Bacterial hemolysis destroys the cell membranes of the red blood cells. Once the cell opens, haemoglobin molecules come out. Beta hemolysis occurs due to a bacterial enzyme called beta hemolysin. Bacteria-producing beta hemolysin is known as beta-hemolytic bacteria, and the common species are S. pyogenes and S. agalactiae.

When these bacteria are grown in blood agar medium, they release beta hemolysin into the medium. Beta hemolysins breakdown the red blood cells completely. Hence, clear zones are produced around the bacterial colonies. The production of clear zones around the bacterial colonies is the trait used in the identification of beta-hemolytic bacteria.

What is Gamma Hemolysis?

Gamma hemolysis is the third type of hemolysis reaction. It refers to the non-destruction of red blood cells. This is due to the absence of hemolysin. Organisms do not produce hemolysin enzymes that are essential for the breakdown of red blood cells. When there is no hemolysin enzyme, the breakdown of red blood cells does not take place. Therefore, in gamma hemolysis, no clearing will take place.

Bacterial species that cause gamma hemolysis are known as gamma hemolytic or non-hemolytic bacteria. Gamma hemolysis is a characteristic of Enterococcus faecalis. In fact, the whole genus of Enterococcus is classified as gamma-hemolytic.

What are the Similarities Between Alpha Beta and Gamma Hemolysis?

• Alpha, beta and gamma hemolysis are the three types of hemolysis.
• They are based on the destruction of red blood cells.
• Blood agar is a common medium used to observe hemolysis.
• Bacteria are responsible for all three types of hemolysis.

What is the Difference Between Alpha Beta and Gamma Hemolysis?

In alpha hemolysis, we observe partial destruction of red blood cells while in beta hemolysis, we can see the complete destruction of red blood cells. However, in gamma hemolysis, the destruction of red blood cells does not take place. So, this is the key difference between alpha beta and gamma hemolysis. Alpha hemolytic bacteria produce alpha hemolysis in alpha hemolysis while beta hemolytic bacteria produce beta hemolysis in beta hemolysis. But, gamma hemolytic bacteria do not produce hemolysins.

The below infographic summarizes the difference between alpha beta and gamma hemolysis.

Summary – Alpha Beta vs Gamma Hemolysis

Hemolysis is the breakdown of red blood cells by bacterial enzymes. Many bacteria are able to produce hemolysin enzymes. There are three types of hemolytic reactions as alpha hemolysis, beta hemolysis and gamma hemolysis. In alpha hemolysis, the incomplete breakdown of red blood cells occurs. Hence, greenish colour zones are produced around the bacterial colonies grown on the blood agar plates. In beta hemolysis, the complete destruction of red blood cells occurs. Hence, clear zones are produced around the bacterial colonies in the blood agar plates. In gamma hemolysis, red blood cells are not destroyed due to the absence of hemolysin enzymes. Hence, no clearing will take place in gamma hemolysis. Thus, this summarizes the difference between alpha beta and gamma hemolysis.

Reference:

1. “Blood Agar, Hemolysis, And Hemolytic Reactions | Encyclopedia.Com”. Encyclopedia.Com, 2020, Available here.
2. “Hemolysis”. En.Wikipedia.Org, 2020, Available here.

Image Courtesy:

1. “S. mitis alpha hemolysis” By VeeDunn (CC BY 2.0) via Flickr
2. “Beta hemolysis on blood agar” By HansN. – Own work (CC BY-SA 3.0) via Commons Wikimedia
3. “Hemolysis types” By Mibilehre – Own work (CC BY-SA 4.0) via Commons Wikimedia