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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.
Other enterobacteria such as E. coli will ferment the lactose present in the medium to an extent that will prevent pH reversion by decarboxylation and acidify the medium, turning it yellow. Salmonella species: red colonies, some with black centers. The agar itself will turn red due to the presence of Salmonella type colonies. Shigella species ...
OF-glucose deeps contain glucose as a carbohydrate, peptones, bromothymol blue indicator for Hugh-Leifson's OF medium or phenol red for King's OF medium, and 0.5% agar. To perform the OF-glucose test, two tubes of OF-glucose medium are inoculated with the test organism.
Lactose fermenters turn red or pink on MacConkey agar, and nonfermenters do not change color. The media inhibits growth of gram-positive organisms with crystal violet and bile salts, allowing for the selection and isolation of gram-negative bacteria. The media detects lactose fermentation by enteric bacteria with the pH indicator neutral red. [2]
Staphylococcus aureus produces yellow colonies with yellow zones, whereas other coagulase-negative staphylococci produce small pink or red colonies with no colour change to the medium. [4] If an organism can ferment mannitol, an acidic byproduct is formed that causes the phenol red in the agar to turn yellow. [ 1 ]
The pH indicator Methyl Red is added to one tube and a red color appears at pH's lower than 4.2, indicating a positive test (mixed acid fermentation is used). The solution remaining yellow (pH = 6.2 or above) indicates a negative test, meaning the butanediol fermentation is used. The VP test uses alpha-naphthol and potassium hydroxide to test ...
The U.S. Food and Drug Administration (FDA) has officially announced a ban on red dye No. 3, or erythrosine, from foods and oral medications due to a potential cancer risk. Food manufacturers have ...
Raoultella planticola on MacConkey agar, showing a positive result (the microorganism has the ability to degrade lactose, which is detected by the pH indicator neutral red). The technique of the streaking is done by using 13 streaks.