is the breakdown of red blood cells. The ability of bacterial colonies to induce hemolysis when grown on blood agar is used to classify certain microorganisms. This is particularly useful in classifying streptococcal
Streptococcus is a genus of spherical Gram-positive bacteria belonging to the phylum Firmicutes and the lactic acid bacteria group. Cellular division occurs along a single axis in these bacteria, and thus they grow in chains or pairs, hence the name — from Greek στρεπτος streptos, meaning...
species. A substance that causes hemolysis is a hemolysin
Hemolysins are exotoxins produced by bacteria that cause lysis of red blood cells in vitro. Visualization of hemolysis of red blood cells in agar plates facilitates the categorization of some pathogenic bacteria such as Streptococcus and Staphylococcus...
When Alpha hemolysis
(α-hemolysis) is present the agar under the colonies is dark and greenish. Streptococcus pneumoniae
Streptococcus pneumoniae, or pneumococcus, is Gram-positive, alpha-hemolytic, aerotolerant anaerobic member of the genus Streptococcus. A significant human pathogenic bacterium, S...
and a group of oral streptococci (Streptococcus viridans
Viridans Streptococcus is a pseudotaxonomic non-Linnaenan term for a large group of commensal streptococcal bacteria that are either α-hemolytic, producing a green coloration on blood agar plates , or nonhemolytic...
or viridans streptococci) 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 caused by hydrogen peroxide
A peroxide is a compound containing an oxygen–oxygen single bond or the peroxide anion .The O−O group is called the peroxide group or peroxo group. In contrast to oxide ions, the oxygen atoms in the peroxide ion have an oxidation state of −1.The simplest stable peroxide is hydrogen peroxide...
produced by the bacterium, oxidizing hemoglobin
Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates, with the exception of the fish family Channichthyidae, as well as the tissues of some invertebrates...
to green methemoglobin.
(β-hemolysis), sometimes called complete hemolysis
, is a complete lysis of red cells in the media around and under the colonies: the area appears lightened (yellow) and transparent. Streptolysin, an exotoxin, is the enzyme produced by the bacteria which causes the complete lysis of red blood cells. There are two types of streptolysin: Streptolysin O (SLO) and streptolysin S (SLS). Streptolysin O is an oxygen-sensitive cytotoxin, secreted by most Group A streptococcus (GAS), and interacts with cholesterol in the membrane of eukaryotic cells (mainly red and white blood cells, macrophages, and platelets), and usually results in β-hemolysis under the surface of blood agar. Streptolysin S is an oxygen-stable cytotoxin also produced by most GAS strains which results in clearing on the surface of blood agar. SLS affects immune cells, including polymorphonuclear leukocytes and lymphocytes, and is thought to prevent the host immune system from clearing infection. Streptococcus pyogenes
Streptococcus pyogenes is a spherical, Gram-positive bacterium that is the cause of group A streptococcal infections. S. pyogenes displays streptococcal group A antigen on its cell wall. S...
, or Group A beta-hemolytic Strep (GAS), displays beta hemolysis.
Some weakly beta-hemolytic species cause intense beta hemolysis when grown together with a strain of Staphylococcus
Staphylococcus is a genus of Gram-positive bacteria. Under the microscope they appear round , and form in grape-like clusters....
. This is called the CAMP test
The CAMP test is a test to identify Group B β-streptococci based on their formation of a substance that enlarges the area of hemolysis formed by β-hemolysin from Staphylococcus aureus...
. Streptococcus agalactiae
Streptococcus agalactiae is a beta-hemolytic Gram-positive streptococcus.- Identification :The CAMP test is an important test for identification...
displays this property. Clostridium perfringens
Clostridium perfringens is a Gram-positive, rod-shaped, anaerobic, spore-forming bacterium of the genus Clostridium. C. perfringens is ever present in nature and can be found as a normal component of decaying vegetation, marine sediment, the intestinal tract of humans and other vertebrates,...
can be identified presumptively with this test.
If an organism does not
induce 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
Enterococcus faecalis – formerly classified as part of the Group D Streptococcus system – is a Gram-positive, commensal bacterium inhabiting the gastrointestinal tracts of humans and other mammals. It is among the main constituents of some probiotic food supplements. Like other species in the genus...
(formerly called Group D Strep) displays gamma hemolysis.