SIMMONS CITRATE AGAR SLANT (10 Slants)

Simmons Citrate Agar Slant is a selective medium designed for differentiation of Gram-negative bacteria that use citrate as its sole carbon source. It is especially good for separation of faecal coliforms and aerogenes groups and is suggested for testing of enteric Gram-negative bacillus from the laboratory, water and food samples.
The medium has ammonium dihydrogen phosphate as the only source of nitrogen and sodium citrate as the only source of carbon. Dipotassium phosphate acts as a buffer and sodium chloride provides osmotic balance. Magnesium sulfate is a cofactor in many metabolic pathways and agar acts as the solidifying agent. This nutrient selectivity enables growth of only those organisms that can use citrate and ammonium salts as substrates on the medium.
In citrate fermentation, bacteria break down citrate and utilize the ammonium salt as a source of nitrogen, leading to the formation of alkaline products including ammonia. The resultant alkalinity of the medium causes the bromothymol blue indicator to turn from green to blue at alkaline pH. Organisms unable to utilize citrate generally show no significant growth or colour change.
The differential growth and colour reaction is a convenient biochemical marker to differentiate enteric Gram negative bacilli in routine microbiological identification.

Differentiates Gram-negative bacteria through citrate utilization, with growth and a characteristic colour change indicating positive citrate metabolism.