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f9488a8cf8 The slanted shape of this medium provides an array of surfaces that are either exposed to oxygen-containing air in varying degrees (an aerobic environment) or not exposed to air (an anaerobic environment). Carbon dioxide, if produced, may not show as bubbles because it is far more soluble in the medium. Under anaerobic conditions (as occur toward the bottom of the tube) some bacteria use thiosulfate as an electron acceptor and reduce it to hydrogen gas. The blackening of the medium is almost always observed in the butt (bottom) of the medium. The Triple Sugar Iron (TSI) test is a microbiological test roughly named for its ability to test microorganism's ability to ferment sugars and to produce hydrogen sulfide. It is often used in the selective identification of enteric bacteria including Salmonella and Shigella. Retrieved 2008-11-17. If this occurs, the newly formed hydrogen sulfide (H 2S) reacts with ferrous sulfate in the medium to form ferrous sulfide, which is visible as a black precipitate. Whereas if it ferments both lactose and glucose, it results in a yellow/yellow tube and remains that way due to the large amount of acid produced in the reaction. Disqus - Download Calendar Jawa 2015 Pdf Map.
.. Bacteria that ferment any of the three sugars in the medium will produce byproducts. These byproducts are usually acids, which will change the color of the red pH-sensitive dye (phenol red) to a yellow color. Various reactions seen in TSI agar . Blackening of the bottom due to H2S production may mask the acid reaction (yellow) in the bottom of the tube. Position of the color change distinguishes the acid production associated with glucose fermentation from the acidic byproducts of lactose or sucrose fermentation. Many bacteria that can ferment sugars in the anaerobic butt of the tube are enterobacteria. The TSI slant is a test tube that contains agar, a pH-sensitive dye (phenol red), 1% lactose, 1% sucrose, 0.1% glucose, as well as sodium thiosulfate and ferrous sulfate or ferrous ammonium sulfate. Interpretation of results.