n BD Fluid Thioglycollate Medium, glucose, peptone, and yeast extract provide the growthfactors necessary for bacterial growth. Sodium thioglycollate and L-cystine are reducing agentthat prevent the accumulation of peroxides which are lethal to some microorganisms. Resazurinis an oxidation-reduction indicator, being pink when oxidized and colorless when reduced. Thesmall amount of agar assists in the maintenance of a low redox potential by stabilizing themedium against convection currents, thereby maintaining anaerobiosis in the lower depths of themedium.8 Due to its agar content, Fluid Thioglycollate Medium often appears slightly opaque.The ready-to-use medium described in this document is filled under a stream of nitrogen gas,resulting in a decoloration of the reazurin indicator. However, the media may be used untilapproximately 30% of the medium (top layer) has been oxidized, as indicated by a pink color ofthe resazurin near the surface. If oxidation has proceeded further, the broth may be reheatedonce in steam or boiling water, cooled and used.