Godsey et al. supported their findings in an evaluation of methods based on microbial enzyme activity profiles³. Most strains of E. coli produce an enzyme β-D-glucuronidase. In the indole test, the enzyme tryptophanase attacks tryptophan molecule on its side chain, leaving the aromatic ring in the form of indole. The indole is then detected by addition of ρ-dimethylamino-benzaldehyde (Kavocs’ Reagent) which produces a red color. β-D-glucuronidase is an enzyme that cleaves the substrate 4-methylumbelliferyl-β-D-glucuronide (MUG) and thereby produces a fluorescent product called methylumbelliferone⁴. This compound is detectable using a long wave ultraviolet light (360 nm).

• Ready to use - 4-methylumbelliferyl- β-D-glucuronide-impregnated disk
• Easy to store - No special storage required
• Easy to interpret - With visual inspection
  • In MUG Disk test, examine the disk for fluorescence using a longwave ultraviolet light (360nm) in a darkened room. Blue fluorescence is interpreted as positive test.
  • In Indole test, add one drop of Kovacs‘ Indole Reagent to the disk and immediately observe for red color development.

Interpretation:

MUG Disk Test (Direct or Tube Test):

Positive test - Blue fluorescence observed under 360 nm UV light

Negative test - No fluorescence observed under 360 nm UV light

Indole Test:

Positive test - Red color development on the disk or in the tube

Negative test - No red color development on the disk or in the tube