Iodine Reagent

 

Iodine reagent is used to detect the presence of starch in a growth medium. When it is added to starch agar plates, the iodine reagent combines with starch in the medium to produce a blue-brown color. Bacteria producing alpha-amylase, an enzyme destroying starch, exhibit clear halos under their growth indicating that the starch has been digested. When iodine reagent is added to an overnight culture of a microbe unable to break down starch, the medium is converted to a uniformly blue-brown color.