What is the result of complete hemolysis on a blood agar plate?

Complete hemolysis on a blood agar plate results in a clear zone around the bacterial growth. This clear area indicates the complete lysis of red blood cells and the breakdown of hemoglobin by bacterial enzymes, typically produced by certain species of bacteria such as Streptococcus pyogenes.

When bacteria that exhibit complete hemolysis grow on blood agar, they secrete hemolysins that lyse the red blood cells in the surrounding area. As a result, there is a visible change in the agar around the colonies, transitioning from its original red color to a clear appearance. This differentiation is crucial for identifying pathogenic bacteria and understanding their virulence.

The other options describe different types of hemolysis or reactions on blood agar. For example, a greenish zone indicates partial hemolysis (alpha hemolysis), while no change or a yellow coloration does not relate to hemolytic activity and are not characteristic of complete hemolysis.