Simmons Citrate Agar

Item No.  NCM0168A

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Simmons Citrate Agar is used for the differentiation of microorganisms on the basis of citrate utilization in a laboratory setting. Simmons Citrate Agar is not intended for use in the diagnosis of disease or other conditions in humans.

Koser first developed a liquid medium for differentiating coliforms from fecal coliforms. Fecal coliforms were unable to use citrate as the sole source of carbon and inorganic ammonium salt as a sole source of nitrogen. Non-fecal coliforms, such as Enterobacter aerogenes could use citrate in such a medium with resultant alkalinity. Liquid medium had the disadvantage of appearing turbid when a large inoculum was used, although no growth had taken place. This observation led Simmons to devise a solid medium that eliminated the problem with turbidity.

Simmons Citrate Agar is a modification of Koser’s medium, with the addition of bromothymol blue and 1.5% agar. Organisms able to metabolize citrate grow luxuriantly. The medium is alkalinized and changes from green to deep blue in 24 – 48 hours. Escherichia coli either do not grow at all on this medium or grow so sparsely that no change in reaction is apparent. Simmons Citrate Agar is recommended for differentiation of enteric Gram-negative bacilli from laboratory specimens, water samples, and food samples.

Analyte Non-selective
Brand NEOGEN® Culture Media
Formula Liter
Ammonium Dihydrogen Phosphate 1.0 g/L
Dipotassium Phosphate 1.0 g/L
Sodium Chloride 5.0 g/L
Sodium Citrate 2.0 g/L
Magnesium Sulfate 0.2 g/L
Bromothymol Blue 0.08 g/L
Agar 15.0 g/L
Grams per Litre 24.20
Litres per 500g 21.00
Mass 500 g
Package Dimensions 4.60 IN x 2.90 IN x 8.60 IN
Package Weight 1.35 LB
Plates per 500g 1,130.00
  1. Suspend 24.2 g of the medium in one liter of purified water.
  2. Heat with frequent agitation and boil for one minute to completely dissolve the medium.
  3. Dispense into tubes and autoclave at 121ºC for 15 minutes.
  4. After autoclaving, allow medium to solidify in a slant position.
Previous Item Number Product was previously known as Acumedia Product: 7156 Simmons Citrate Agar; and LabM Product: LAB069 Simmons Citrate Agar