Evaluation of the β-Glucuronidase Substrate 5-Bromo-4-Chloro-3-Indolyl-β-D-Glucuronide (X-GLUC) in a 24-Hour Direct Plating Method for Escherichia coli

Abstract

A 24-h direct plating method for Escherichia coli using Peptone-Tergitol agar was used to compare the effectiveness of the chromogenic substrate 5-bromo-4-chloro-3-indolyl-β-D-glucuronide (X-GLUC) with the fluorogenic substrate 4-methylumbelliferyl-β-D-glucuronide (MUG) for β-glucuronidase activity. Values obtained for enumeration of two strains of E. coli recovered from artificially inoculated raw minced chicken (i.e., plating efficiencies on the inoculum, cells per g, and recovery percentages elated to those on Plate Count Agar) indicate that X-GLUC at 50 μg/ml was as effective as MUG in an agar medium. Unlike MUG, X-GLUC does not require ultraviolet light illumination, and the color reaction produced remains localized in the positive colonies.