X-GlcU (5-Bromo-4-chloro-3-indolyl-β-D-glucuronide, cyclohexylammonium salt), also known as BCIG, is a chromogenic β-glucuronidase substrate widely used for monitoring E. coli contamination in food (such as meat, dairy products and shellfish, etc) and water, and for the detection of GUS gene expression in plants. X-GlcU also has clinical applications in the assessment of urinary tract infection by detecting the presence of E. coli. The substrate yields a dark blue (λmax 615 nm) precipitate after enzymatic hydrolysis.
