Koser Citrate Broth is used to differentiate Escherichia coli from the Enterobacter group on the basis of citrate use utilization. It is used in the same way as Simmons Citrate Agar (Cat. 1014), with the advantage of differentiating between coliforms of fecal origin (the majority is citrate-negative) and organisms from dirt that are 90% positive according to Wilson and Miles. These same authors report that only 6,7% of the coliforms isolated from human or animal feces are citrate-positive. Enterobacter aerogenes and Enterobacter cloacae use sodium citrate as a source of carbon and the inorganic ammonium phosphate salt as a source of nitrogen. Escherichia coli cannot use sodium citrate as carbon source and does not grow in this medium. Biochemical identification methods for identifying E. coli frequently include Koser citrate. Magnesium sulphate is a magnesium ion required in a large variation of enzymatic reactions, including DNA replication. Monopotassium phosphate is a buffer.
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