Classification

Alpha

In alpha hemolysis, the red blood cells remain intact, but the hemoglobin is converted to biliverdin. This causes dark greening of the blood agar plate around the colonies.
Pneumococci
S. pneumoniae: Causes bacterial pneumonia, otitis media and meningitis.

Beta hemolysis is a complete hemolysis of erythrocytes by the enzyme hemolysin.
Clear zones will appear around the colonies on the blood agar plate.
Beta-hemolytic Streptococci are further divided into serological groups using specific antibodies that recognize surface carbohydrate antigens
Group A Streptococcus S. pyogenes: Causes infections like strep throat, acute rheumatic fever, scarlet fever, acute glomerulonephritis and necrotizing fasciitis. Other Streptococci species may also possess the Group A antigen but are not human pathogens. These include S. dysgalactiae subsp. equisimilis and S. anginosus strains.
Group B Streptococcus S. agalactiae: Causes meningitis in neonates and the elderly. Occasionally colonizing the female reproductive tract, they increase the risk for premature rupture of membranes and transmission of the infection to the child.
Group C Streptococcus S. equi: Causes strangles infection in horses.
S. zooepidemicus: Causes infections in cattle, horses and other mammals.
Group D Streptococcus (Enterococci)
Many former Group D Streptococci have been reclassified to the genus Enterococcus (e.g. S. faecalis, S. faciem, S. durans, S avium).
S. bovis and S. suis: Still in the Group D streptococci.

Gamma hemolysis is a misnomer as there is actually no hemolysis. Non-hemolytic or gamma-hemolytic Streptococci rarely cause disease.