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Glucose – a monosaccharide Lactose – a disaccahride glucose + galactose

Glucose – a monosaccharide Lactose – a disaccahride glucose + galactose Fermentation can produce acid and/or gas A heterofermenter produces large amounts of several acids A homofermenter produces a small amount of a single acid Phenol red becomes yellow in acid. CITRATE UTILIZATION.

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Glucose – a monosaccharide Lactose – a disaccahride glucose + galactose

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  1. Glucose – a monosaccharide • Lactose – a disaccahride glucose + galactose • Fermentation can produce acid and/or gas • A heterofermenter produces large amounts of several acids • A homofermenter produces a small amount of a single acid • Phenol red becomes yellow in acid

  2. CITRATE UTILIZATION • Catabolism of citrate produces sodium carbonate, which is basic, so pH increases • The change in the pH is indicated by the dye bromphenol blue in the medium, which changes from green to blue • Also see growth of the cells • The citrate is brought into the cells by citrate permease

  3. UREA CATABOLISM • Urea is broken down by urease to CO2 plus ammonia (NH3) • Ammonia is basic, so raises the pH, which changes the phenol red to deep pink

  4. H2S PRODUCTION AND DETECTION • Produced from the amino acid cysteine, which contains sulfur • H2S reacts with iron (Fe) to form FeS (iron sulfide), which is a black precipitate • Also detects mobility of the bacteria, by spread of the black precipitate from the stab line

  5. INDOLE PRODUCTION • Indole is produced by the catabolism of the amino acid tryptophan • Addition of Kovac’s reagent produces a red color

  6. MR-VP TESTS • Methyl red – detects high level of acid production • Changes color at pH5 • (Phenol red changes color at pH 6.8) • V-P – detects the production of a particular alcohol (butanediol) that is made by Enterobacter. Addition of Barritt’s reagent produces a red color • Both the acid and the alcohol are products of glucose fermentation

  7. The IMViC series of tests is used to detect sewage contamination (for example of ocean water)

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