Additive for selective media for Staphylococcus, Corynebacterium, Streptococcus and Vibrio. Its function is to prevent the growth of most gram-negative and those gram-positive incapable of reducing tellurite. Added to media such as Giolitti Cantoni Broth Art No. 02-230 and Vogel-Johnson Agar Art.No. 01-206.r