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Simmons Citrate Agar

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 bromthymol 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.

 

Formula Liter
Ammonium Dihydrogen Phosphate 1 g
Dipotassium hosphate 1 g
Sodium Chloride 5 g
Sodium Citrate 2 g
Magnesium Sulfate 0.2 g
Bromthymol Blue 0.08 g
Agar 15 g

Final pH: 6.9 ± 0.2 at 25°C
Formula may be adjusted and/or supplemented as required to meet performance specifications.

Directions

  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 121°C for 15 minutes.
  4. After autoclaving, allow medium to solidify in a slanted position.

Order Details

Product # Product Description
7156A Simmons Citrate Agar, 500 g
7156B Simmons Citrate Agar, 2 kg
7156T Simmons Citrate Agar, 5 kg