Transcript Lab Hydrogen Sulfide Production

H2S production
hydrogen sulfide production
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Amino acid cystine (substrate)
Cystine desulfhydrase – enzyme
Hydrogen sulfide (product)
Medium has iron – indicator for hydrogen
sulfide
• Hydrogen sulfide combines with iron to
make a black precipitate
IMViC test
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I – indole
M – methyl red
V – Voges – Proskauer
C – citrate
Differentiate E.coli from E. cloacae and K.
pneumoniae
Indole test
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Tryptophan – amino acid – substrate
Tryptophanase – enzyme
Indole – product
Add dropperful of Kovac’s reagent
Top segment of the medium - red
Methyl red
• Some bacteria ferment glucose and release
acids
• Add 10 drops of methyl red
• Medium is red – positive for acid
• Voges – Proskauer test
• Some bacteria ferment glucose and release
Acetyl methyl carbinol
• Add 10 drops of barritt’s reagent A and barritt’s
reagent B
• Red/pink color in the medium - positive
Citrate
• Can the bacteria use citrate as the only source
of carbon?
• Medium has the pH indicator – bromthymol blue
• Green – neutral
• Blue – basic
• Yellow – acidic
• When bacteria use citrate ammonium ions are
released.
• Environment becomes basic - blue
• Urea hydrolysis
• Some bacteria make urease and break
down urea.
• Ammonium ions are released
• Medium becomes basic
• pH indicator becomes fuchsia
Motility
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Negative
Distinct line of growth in the medium
Growth is concentrated along the stab line.
These bacteria have no choice but to stay
along the line because they have no
flagella to move away.
• Positive
• Diffused growth
• Growth is not concentrated along the stab
line
• Medium is cloudy
• Bacteria have flagella and help them to
move into the medium and grow
throughout the medium