To test for hydrogen sulfide production, a medium with a sulfur-containing compound and iron salts is inoculated and incubated. It can be used to detect hydrogen sulfide production, indole production, and motility. Soy agar cultures of Proteus mirabilis, Escherichia coli , and Enterobacter cloacae . Incubate at 37C until the next lab period. Next lab period add Kovac's reagent to each tube to detect indole production.
Water is then a harmless end product.
This is done by the enzyme catalase breaking the hydrogen peroxide into water and oxygen as shown above. This appears as foaming . When iodine is added to starch, the iodine-starch complex which forms gives a characteristic dark brown or deep purple color reaction . If the starch has been hydrolyzed into glucose molecules by the diastase exoenzyme, it no longer gives this reaction. Therefore, flood the surface of the Starch agar plate with gram's iodine .