Simmons and Koser’s citrate: Introduction, Differences, and Keynotes

Introduction of Simmons and Koser’s citrate

Simmons citrate medium is a solid medium due to having agar. It is also an indicator medium due to the presence of phenol red. To say test positive, there should be growth and color change of the medium.

Koser’s citrate medium is a liquid medium lacking agar. It does not contain any indicator. A positive test is shown by the presence of turbidity in the medium. It is a highly sensitive test than other media.

Differences in Simmons and Koser’s citrate medium

The differences between Simon’s and Koser’s citrate are as follows-

Simmons citrate	Koser’s citrate
It is a solid medium.	It is a liquid medium.
It contains agar.	It does not contain agar.
It has a bromothymol blue indicator.	It does not contain any indicator.
A positive test shows both growth and color change.	A positive test shows turbidity in the medium.
It is less sensitive.	It is highly sensitive.

Citrate-positive bacteria (blue), negative (no color change)

Keynotes

• Christen’s citrate medium is the same as Simmons’s citrate medium in which the bromothymol blue indicator is replaced by phenol red.
• Citrate-positive bacteria are Klebsiella pneumoniae, Citrobacter freundii, and Enterobacter cloacae (a minority of strains gives negative results), Salmonella other than Typhi and Paratyphi A, Serratia marcescens, Proteus mirabilis(a minority of strains gives negative result), Providencia alcalifaeciens, Vibrio vulnificus, Euringella Americana and Achromobacter oxylosoxidans.
• Citrate test variable (different strains give different results) bacteria are Proteus vulgaris, Vibrio cholerae, and Vibrio parahaemolyticus.
• Citrate test-negative organisms are Escherichia coli, Shigella species, Salmonella Typhi, Salmonella Paratyphi A, Morganella morganii, Yersinia enterocolitica, Edwardsiella tarda, and Vibrio holisae.
• Other methods of citrate utilization test available are-IMViC the test kit method and the API test kit method.