Sterile Thioglycolate Broth Ph. Eur., USP, ISO 7937, for microbiology Thioglycolate Broth is used for detecting microorganisms in sterility tests, according to the formula specified in the USP and conforms to formulations detailed in the Bristish and European Pharmacopoeia. The reducing agents thioglycolate and L-Cystine ensure anaerobiosis which is adequate even for fastidious anaerobes. In this broth a special agar with a high viscosity but a very low turbidity is used. A very slow cooling is recommended to prevent stratification. The higher viscosity of the fluid thioglycolate medium prevents rapid uptake of oxygen. Any increase in the oxygen content is indicated by the redox indicator sodium resazurin which changes colour to pink. The -SH groups of these substances also inactivate arsenic, mercury and other heavy metal compounds. Thioglycolate media are thus suitable for the examination of materials which contain heavy metals or heavy metal preservatives.