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• 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
• 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
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
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
INDOLE PRODUCTION
• Indole is produced by the catabolism of the
amino acid tryptophan
• Addition of Kovac’s reagent produces a red
color
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
The IMViC series of tests is used to detect sewage
contamination (for example of ocean water)
Escherichia
coli
Enterobacter
aerogenes
Indole
Methyl Red
V-P
Citrate
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