 TSI agar medium was developed based on Kligler's iron agar, which had been used for the determination of lactose-fermentative bacteria, by addition of sucrose to be able to detect sucrose-fermentative bacteria, also.Bacteria that ferment any of the three sugars in the medium will produce byproducts.These byproducts are usually acids, which will change the color of the red pH-sensitive dye (phenol red) to a yellow color.