What color change indicates the presence of β-hemolysis, used to differentiate certain Haemophilus species?

The presence of β-hemolysis is indicated by a color change from yellow to clear. This observation reflects the breakdown of red blood cells and the liberation of hemoglobin in the surrounding medium, leading to a transparent area around the bacterial colonies on a blood agar plate. In the context of differentiating certain Haemophilus species, β-hemolytic strains will effectively lyse red blood cells, resulting in this notable clear zone. This is a critical characteristic used in microbiological diagnostics to identify and confirm the presence of specific bacteria within the Haemophilus genus.

The other color changes listed do not accurately represent the specific hemolytic activity associated with Haemophilus species and therefore are not relevant in this context.