What is an indicator of alpha hemolysis?

Alpha hemolysis is characterized by the partial breakdown of red blood cells in the surrounding area on a blood agar plate, which leads to a greenish discoloration around the colonies of certain bacteria, like Streptococcus pneumoniae or Streptococcus mitis. This greenish tint is due to the conversion of hemoglobin to methemoglobin, indicating that while there is some lysis of red blood cells, it is not complete.

The other options refer to different processes: complete breakdown of red blood cells is indicative of beta hemolysis, where there is a clear zone around the bacterial growth; no change in red blood cells aligns with gamma hemolysis (or non-hemolysis), where bacterial growth does not affect the appearance of the blood agar; and the presence of white blood cells is unrelated to hemolysis and typically indicates an immune response rather than a specific type of hemolysis. Therefore, the presence of greenish discoloration is specifically indicative of alpha hemolysis.