The presence of indole is detected by adding kovacs

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The Presence of Indole is detected by adding Kovac’s Reagent, which consists of p-Dimethylaminobenzaldehyde (DMBA), HCl, and Amyl Alcohol. The DMBA reacts with Indole to form a Cherry Red Rosindole Dye. Since this Dye will remain in the Amyl Alcohol -- which is insoluble in Water -- a Positive Indole Test results in a Red Layer of Rosindole in the Amyl Alcohol Layer at the Top of the Tube. All you’ll do in Today’s Lab is inoculate separate Tubes of Tryptone Broth with your E. coli and/or your Enterobacter . Next Time you’ll add Kovac’s Reagent. E. coli is Indole Positive and will produce a Red Layer of Rosindol Dye in the Amyl Alcohol Layer at the Top of the Tube. Enterobacter is Indole Negative and will not produce any Dye in the Amyl Alcohol at the Top of the Tube so this Layer will remain Yellowish.
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Lab 6 Page 28 Methyl Red/Voges-Proskauer The Methyl Red/Voges-Proskauer Tests together determine whether Enteric Bacteria are Mixed Acid Fermenters of Glucose or Butanediol Fermenters of Glucose. You’ll be inoculating a Single Tube of MR-VP Medium with each Bacterium in Today’s Lab. This Medium contains Tryptone, Glucose, and a Phosphate Buffer. In the next Lab we’ll split the Contents of this Tube into separate Tubes and perform separate Methyl Red and Voges-Proskauer Tests. Methyl Red (Atlas Page 82) “Is this Bacterium a Mixed-Acid Fermenter?” Mixed Acid Fermenters of Glucose will produce Carbon Dioxide, Hydrogen, and Ethanol, as well as large Amounts of stable Acids, particularly Acetic Acid, Formic Acid, Lactic Acid, and Succinic Acid. After a 48 Hour Incubation in MR-VP Medium, we’ll add a Methyl Red pH Indicator. E. coli is Methyl Red Positive. The Presence of stable Acids should pull the pH down to somewhere below pH 4.4, where Methyl Red will remain Red. Red is Positive for the Methyl Red Test. Ideally, we should be incubating our MR-VP Broth for between 2 and 5 Days to get Good Reactions. But this is not an Ideal World and MIC 101 is not an Ideal Lab so expect your Methyl Red Positive to be sort of a Jolly Rancher Watermelon Color. Enterobacter is Methyl Red Negative. The Absence of stable Acids will result in a Neutral to mildly acidic Medium, where Methyl Red will be a mysterious Tropical Fruit Color, which is best described as Dried Mango. (Sorry but it won’t be a Lemon Yellow like in Figure 7-63 in your Atlas.) Voges-Proskauer (Atlas Page 98) “Is this Bacterium a Butanediol Fermenter?” Butanediol Fermenters of Glucose will produce all manner of Acids, but most of these aren’t sufficiently stable to stick around and overcome the Phosphate Buffer in the MR-VP Broth. However, Butanediol Fermenters of Glucose will produce large Amounts of Acetoin and 2,3-Butanediol. The Acetoin and 2,3-Butanediol can be detected by adding α -Naphthol and KOH.
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