H2S productionhydrogen sulfide production

• 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

• I – indole

• M – methyl red

• V – Voges – Proskauer

• C – citrate

• Differentiate E.coli from E. cloacae and K. pneumoniae

Indole test

• 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

• 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