Alpha-hemolytic species cause oxidization of iron in hemoglobin molecules within red blood cells, giving it a greenish color on blood agar. Beta-hemolytic species cause complete rupture of red blood cells. On blood agar, this appears as wide areas clear of blood cells surrounding bacterial colonies. Gamma-hemolytic species cause no hemolysis.Beta-hemolytic streptococci are further classified by Lancefield grouping, a serotype classification (that is, describing specific carbohydrates present on the bacterial cell wall). The 21 described serotypes are named Lancefield groups A to W (excluding I and J). This system of classification was developed by Rebecca Lancefield, a scientist at Rockefeller University.In the medical setting, the most important groups are the alpha-hemolytic streptococci S. pneumoniae and Streptococcus viridans group, and the beta-hemolytic streptococci of Lancefield groups A and B (also known as “group A strep” and “group B strep”). Table: Medically relevant streptococci (not all are alpha-hemolytic)

Alpha-hemolytic
When alpha-hemolysis (α-hemolysis) is present, the agar under the colony will appear dark and greenish due to the conversion of hemoglobin to green biliverdin. Streptococcus pneumoniae and a group of oral streptococci (Streptococcus viridans or viridans streptococci) display alpha-hemolysis. Alpha-hemolysis is also termed incomplete hemolysis or partial hemolysis because the cell membranes of the red blood cells are left intact. This is also sometimes called green hemolysis because of the color change in the agar. Pneumococci
S. pneumoniae (sometimes called pneumococcus), is a leading cause of bacterial pneumonia and occasional etiology of otitis media, sinusitis, meningitis, and peritonitis.
See also
Cia-dependent small RNAs
Quellung reaction
Streptococcal infection in poultry
Streptococcal pharyngitis
Streptokinase

References
External links
Centers for Disease Control Prevention (CDC) (March 2000). "Adoption of perinatal group B streptococcal disease prevention recommendations by prenatal-care providers—Connecticut and Minnesota, 1998". MMWR Morb. Mortal. Wkly. Rep. 49 (11): 228–32. PMID 10763673. Nature-Inspired CRISPR Enzyme Discoveries Vastly Expand Genome Editing . On: SciTechDaily. June 16, 2020. Source: Media Lab, Massachusetts Institute of Technology. Streptococcus genomes and related information at PATRIC, a Bioinformatics Resource Center funded by NIAID
The Canadian Strep B Foundation Archived 2013-05-02 at the Wayback Machine
The UK Group B Strep Support charity