From figure shows triple
sugar iron agar. What biochemical characteristics does this figure
illustrate? How could this medium be used to begin the identification
of the isolated bacteria in this chapter’s Case Study?
“Triple sugar iron test” is one of the “biochemical tests” used to test the ability of microbe in fermenting the sugars (“glucose, lactose, and sucrose”), and producing hydrogen sulfide. It is commonly used to differentiate among enteric bacteria.
TSI is used to distinguish organisms based on the variation in the pattern of carbohydrate fermentation and “hydrogen sulfide” production. TSI is a “differential medium” consists of lactose, sucrose, glucose in small amounts, “ferrous sulfate” and the “phenol red” as a “pH indicator”. Gas production and the medium’s color change from yellow will indicate the carbohydrate fermentation.
Due to the formation of acid during fermentation, there is a fall in pH. Phenol red is used to detect the “fermentation of carbohydrates” which is showed by the medium’s color changes from orange-red to yellow in the presence of acids. In the case of “oxidative decarboxylation of peptone,” “alkaline products” will be formed and there is a rise in pH. This is showed by the color change of orange-red to deep red. The presence of “sodium thiosulfate” and “ferrous ammonium sulfate” spots the production of “hydrogen sulfide” and is shown by the black color in the butt portion of the tube.
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