Question

What is hemolysis? What are the types of hemolysis?

Answer 1

Hemolysis: Hemolysis may be defined simply as the lysis or the breakdown of erythrocytes or red blood cells. Any substance that can induce hemolysis is called hemolysin. Various kinds of hemolysin are present in bacteria, especially in streptococcal species. Thus hemolysis may occur during a bacterial infection.

The ability of a micro organism to induce hemolysis is a useful way of classification. Bacterial colonies are grown on blood agar medium and their hemolytic capabilities are noted and classified accordingly.

Hemolysis of the following three types are observed on growing bacterial colonies on blood agar medium:

Alpha hemolysis: This kind of hemolysis shows the presence of dark and greenish agar under the bacterial colonies. It is produced as a result of the hydrogen peroxide produced by the colonies which oxidizes hemoglobin in the RBC to green colored methemoglobin. It is also called incomplete or partial hemolysis and is found in case of Streptococcus pneumoniae and certain oral streptococci.

Beta hemolysis: In this kind of hemolysis, there is presence of lightened transparent regions in the agar medium around the bacterial colonies. Hemolysis here occurs due to the presence of the hemolysin called streptolysin which is an exotoxin. Streptolysin are of two types - streptolysin O which is oxygen sensitive and causes lysis of RBCs under the surface of agar and streptolysin S which is oxygen stable and causes lysis of RBCs on the surface of agar. Streptolysin is a cytotoxin responsible for complete breakdown of RBCs and hence beta hemolysis is also known as complete hemolysis. This kind of hemolysis is mainly caused by Group A streptococcus bacteria like Streptococcus pyogenes.

Gamma hemolysis: All non hemolytic colonies which are unable to induce hemolysis in the blood agar are called non hemolytic. They are classified that display gamma hemolysis or no hemolysis. This is shown by a number of species under Staphylococcus genus as well as Enterococcus faecalis. This occurs in the absence of any hemolysin.