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This results in a change of the medium's color from green (neutral) to blue (alkaline). Bacterial colonies are picked up from a straight wire and inoculated into slope of Simmons citrate agar and incubated overnight at 37 °C. Inoculating from a broth culture is not recommended because the inoculum would be too heavy.
It is a defined, selective and differential medium that tests for an organism's ability to use citrate as a sole carbon source and ammonium ions as the sole nitrogen source. After citrate enters a cell through citrate permeases, citrate lyase cleaves it into acetate and oxaloacetate, which is further broken down into carbon dioxide and pyruvate ...
"I" is for indole test; "M" is for methyl red test; "V" is for Voges-Proskauer test, and "C" is for citrate test. The lower case "i" is merely for "in" as the Citrate test requires coliform samples to be placed "in Citrate". These tests are useful in distinguishing members of Enterobacteriaceae. IMViC Results
[9] [4] Citrate is used by S. marcescens to produce pyruvic acid, thus it can rely on citrate as a carbon source and test positive for citrate utilization. [4] In identifying the organism, one may also perform a methyl red test, which determines if a microorganism performs mixed-acid fermentation. S. marcescens results in a
Positive for the phenylalanine test and the Harnstoff urea test; P. vulgaris can test positive or negative for citrate. All combine for a Biocode ID of 31406, (Biocode ID 31402, 31404, 31407 all resulting in P. vulgaris with asymptomatic results) for use in the Interpretation Guide/Computer Coding and Identification System.
Klebsiella aerogenes, [2] previously known as Enterobacter aerogenes, is a Gram-negative, oxidase-negative, catalase-positive, citrate-positive, indole-negative, rod-shaped bacterium. [3] Capable of motility via peritrichous flagella, [ 4 ] it is approximately one to three microns in length.
TCBS agar contains high concentrations of sodium thiosulfate and sodium citrate to inhibit the growth of Enterobacteriaceae. Inhibition of gram-positive bacteria is achieved by the incorporation of ox gall, which is a naturally occurring substance containing a mixture of bile salts and sodium cholate, a pure bile salt.
As there are many bacteria that also look like Salmonella on DCA, it is widely recommended that more selective agars are used for the identification of Salmonella, namely xylose lysine deoxycholate (XLD) agar. This growth medium is heat-sensitive and should be poured and cooled as soon as possible after addition of the deoxycholate, otherwise ...