Simmons Citrate Agar (Dehydrated)

Differentiate members of the family Enterobacteriaceae based on the utilization of citrate with Thermo Scientific™ Oxoid™ Simmons Citrate Agar (Dehydrated). The medium is a solidified form of Koser citrate medium which suffered from the disadvantage that false appearance of growth occurred when large inocula were employed. Simmons¹ modified Koser's formulation by adding agar and bromothymol blue². It complies with the recommendations if the APHA³.

Simmons Citrate Agar is used wither as slopes in test tubes or as a plate medium in petri dishes. Positive growth (i.e. citrate utilization) produces an alkaline reaction and changes the colour of the medium from green to bright blue, while in a negative test (i.e. no citrate utilization) the colour of the medium remains unchanged.

Escherichia coli including serotypes from epidemic infantile enteritis, as well as Shigella, Yersinia and Edwardsiella species do not grow on the medium. Serratia and the majority of the Enterobacter, Citrobacter, Klebsiella, Proteus and Providencia species, except Morganella morganii and Klebsiella rhinoscleromatis utilize citrate and produce the characteristic blue coloration⁴.

Simmons Citrate Agar may be used to differentiate citrate-positive Salmonella enteritidis and members of Salmonella subgenus II, III and IV from the citrate-negative Salmonella typhi, Salmonella paratyphi A, Salmonella pullorum and Salmonella gallinarum.

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