Simmons Citrate Agar slants.
Negative - left and positive - right.
Citrate Utilization Test
J. S. Simmons 1926
DESCRIPTION
Testing the ability of bacteria to utilize sodium or ammonium citrate as sole carbon source. Simmons Citrate Agar medium is the
most used for Enterobacteriaceae identification, together with TSI and MIU media.


Escherichia coli, Shigella spp., Yersinia spp. and Edwardsiella spp. 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
utilise citrate and produce the characteristic blue coloration. Medium may also be used to differentiate Salmonella species (citrate
utilization is a variable character among serovars).
MEDIUM PREPARATION
Composition of Simmons medium:
Magnesium sulphate .........................................................................0.2g
Ammonium (or sodium) phosphate ..................................................1g
Disodic phosphate ...............................................................................1g
Sodium citrate .......................................................................................2g
NaCl ........................................................................................................5g
Bromtymol blue ...............................................................................0.08g
Agar ......................................................................................................15g
H
2O ad 1000 ml,  pH = 6.8-7.2 (other manufacturers specify pH 6.4-6.8). Sterilize by
autoclaving at 121°C for 15 minutes.

The medium may be used either as slopes in test tubes or as a plate medium in Petri
dishes.

PROCEDURE
Pick a well isolated colony and disperse on medium surface. Incubate 24 hours at 37
°C.

RESULTS
Reaction is positive if medium color turn from green to deep blue and negative if
medium remains green.

QUALITY CONTROL
Escherichia coli ATCC 25922: inhibited or no growth, no colour change of medium;
Salmonella Typhimurium ATCC 14028: growth, colour change of medium to blue.
REFERENCES:
1. H. Raducanescu, V.Bica-Popii,1986. Bacteriologie veterinara, Ed. Ceres, Bucuresti.
2. Margaret Barnett, 1992. Microbiology Laboratory Exercises. Wm. C. Brown Publishers.
3. SIMMONS CITRATE AGAR CM0155. Product leaflet, Oxoid.
4. SIMMONS Citrate Agar. Product leaflet,
Merck.
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A demonstration of TSI,MIU and Simmons utilization is available in video section.
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