Simmons Citrate Agar

Differentiate gram-negative bacteria based on citrate utilization using Thermo Scientific™ Remel™ Simmons Citrate Agar. In 1923, Koser developed a liquid medium to differentiate Escherichia coli and Enterobacter aerogenes¹. The medium contained an inorganic ammonium salt and sodium citrate that provided a single nitrogen source and a single carbon source respectively. In 1926, this formulation was modified by Simmons who added 1.5% agar and brom thymol blue indicator².

Gram-negative bacteria that can utilize ammonium dihydrogen phosphate as a sole nitrogen source and sodium citrate as a sole carbon source will grow on Citrate Agar (Simmons). These organisms extract nitrogen from the ammonium salt by breaking it down to form ammonia, leading to alkalization of the medium. This causes the brom thymol blue indicator to change color from green to blue.

• Ready to use – Convenience of prepared medium

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