Differential Reinforced Clostridium Broth is used to determine the count of sulfite-reducing bacteria by the MPN technique. Beef extract, meat peptone and casein peptone provide nitrogen, vitamins, minerals and amino acids essential for growth. Yeast extract is a source of vitamins, particularly of the B-group essential for bacterial growth. Glucose is the fermentable carbohydrate providing carbon and energy. L-Cysteine hydrochloride is the reducing agent. Starch absorbs any toxic metabolites produced. Resazurin is an oxidation indicator, turning from pink (aerobic) to colorless (anaerobic conditions), used as an indicator to monitor anaerobiosis. Ferric ammonium citrate and sodium disulfite are H2S indicators. Clostridium reduce sulfite to sulfide, the iron sulfide produced causes the culture medium to turn black. As other bacteria can also produce sulfide, vegetative forms must first be removed from the culture by a relevant treatment (e.g. pasteurization), and the anaerobic spore-forming microorganisms must then be identified. To inhibit the growth of most non-spore-forming microorganisms add 70 IU/ ml polymyxin to the broth.
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