Starch agar is a differential medium that tests the ability of an organism to produce the extracellular enzymes (exoenzymes) α-amylase and oligo-1,6-glucosidase that are secreted out of the bacteria and diffuse into the starch agar. These enzymes hydrolyze starch by breaking the glycosidic linkages between glucose subunits and allow the products of starch hydrolysis to enter the cell. Starch agar is also used in differentiating members of various genera that have both amylase-positive and amylase-negative species, including Streptococcus, Clostridium, Corynebacterium, Fusobacterium, Enterococcus, Pseudomonas and Bacillus.
