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Although it could be used in other formats (e.g., Petri plates), Simmons' citrate agar is often used in slants or slopes in test tubes. One advantage of using slants over Petri dishes is access to oxygen, which is required by citrate metabolism. Simmons’ agar can be bought from suppliers as ready-made powders or slants.
The TSI slant is a test tube that contains agar, a pH-sensitive dye , 1% lactose, 1% sucrose, 0.1% glucose, [2] and sodium thiosulfate and ferrous sulfate or ferrous ammonium sulfate. All of these ingredients are mixed together, heated to sterility, and allowed to solidify in the test tube at a slanted angle.
The citrate agar is green before inoculation, and turns blue, because of BTB as a positive test indicator, meaning citrate is utilized. The test is also prepared on a slant to maximize bacterial growth for an even better indication of the use of citrate.
Aerobic and anaerobic bacteria can be identified by growing them in test tubes of thioglycolate broth: 1: Obligate aerobes need oxygen because they cannot ferment or respire anaerobically.
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 .
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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 ...
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 ...