Differential Reinforced Clostridial Medium ISO (DRCM) is a medium for the detection and enumeration of the spores of sulfite-reducing anaerobes as described in ISO 26461-1, and is not intended for use in the diagnosis of disease or other conditions in humans. Sulfite reducing anaerobes, in particular Clostridia, can be indicators of remote and intermittent pollution. Widespread in the environment, being found in human and animal feces, soil and waste water, the spores are more resistant to physical and chemical factors than vegetative cells and able to survive for long periods in water. The spores may also be resistant to chlorination at the levels commonly used in water treatment. DRCM has been developed for use with the Most Probable Number (MPN) method to determine the MPN of anaerobes (Clostridia) per volume of sample. The formulation includes peptone, yeast extract, meat extract, starch & L-Cysteine for nutrition with glucose providing the energy source. Sodium acetate provides partial selectivity. Clostridia are able to reduce sulfite to sulfide – forming iron sulfide. Iron (III) citrate is included in the formulation as an indicator of sulfite reduction. Blackening in the medium indicates that iron sulfide has been formed and therefore that sulfite reduction has occurred. Other bacteria are able to form sulfide, so vegetative cells must be first be removed from the test sample by an appropriate process e.g. heat treatment.

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