Description
• Intended Use: Simmons Citrate Agar is used for the differentiation of microorganisms on the basis of citrate utilization.
• Product Summary and Explanation: 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 Kosers 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 clinical specimens water samples, and food
samples.
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