H 2 S production hydrogen 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