Koser's Citrate Medium is supplied by HiMedia. It is a sterile ready prepared media containing 5ml of colourless clear solution in bottles. Koser's Citrate Medium is generally used to differentiate Escherichia coli and Enterobacter aerogenes on the basis of citrate utilization. It is advisable to store this ready prepared media between 2-8C. Composition (in gm/L) is as follows:

Sodium ammonium phosphate (1.50)

Monopotassium phosphate (1.00)

Magnesium sulphate (0.20)

Sodium citrate (3.00)

Coliform bacteria serve as bacterial indicators of sanitary quality of food and wate. Koser Citrate Medium is used as a base for studying citrate utilization tests. This medium is recommended by APHA, to presumptively identify coliforms encountered in the food and dairy industry. The various salts in the medium, serve as source of carbon and nitrogen for the organisms. Citric acid or its sodium salt is utilized as a sole source of carbon and ammonium salt as the sole source of nitrogen by E.aerogenes while E.coli does not utilize these salts and hence fail to grow. Koser Citrate Medium may be used in place of Simmon Citrate Agar. After 24-48 hours incubation, tubes showing marked turbidity may be assumed to contain organisms from aerogenes group and if the medium remains clear it may be considered as coli.