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The color change to blue is useful because growth on Simmons' citrate agar is often limited and would be hard to observe if it were not for the color change. Sometimes, it is possible to detect growth on the Simmons' citrate agar without the accompanying color change to blue. This should be scored as a negative for the citrate use test. [12]
Use of citrate involves the enzyme citrate lyase, which breaks down citrate to oxaloacetate and acetate. Oxaloacetate is further broken down to pyruvate and carbon dioxide (CO 2). Production of sodium bicarbonate (NaHCO 3) as well as ammonia (NH 3) from the use of sodium citrate and ammonium salts results in alkaline pH. This results in a ...
The agar contains citrate and ammonium ions (nitrogen source) and bromothymol blue (BTB) as a pH indicator. [2] Bromothymol blue was added in order to reduce false positives. The citrate agar is green before inoculation, and turns blue, because of BTB as a positive test indicator, meaning citrate is utilized.
[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
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. P. vulgaris can also test urease negative in solid media (such as in Enterotube), but ...
Pseudomonas species also typically give a positive result to the oxidase test, the absence of gas formation from glucose, glucose is oxidised in oxidation/fermentation test using Hugh and Leifson O/F test, beta hemolytic (on blood agar), indole negative, methyl red negative, Voges–Proskauer test negative, and citrate positive. [citation needed]
However, sucrose indirectly produces a positive result with Benedict's reagent if heated with dilute hydrochloric acid prior to the test, although it is modified during this treatment as the acidic conditions and heat break the glycosidic bond in sucrose through hydrolysis. The products of sucrose decomposition are glucose and fructose, both of ...
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. Sodium thiosulfate also serves as a sulfur source and its presence, in combination with ferric citrate, allows for the easy detection of hydrogen ...