Interference by Carbohydrate Substrates, Flavonoids, and Monosaccharide Derivatives on Bacterial β-D-Glucuronidase Assays

Most commercially available test kits for water and foodstuffs use β-galactosidase activity for coliforms and β-glucuronidase activity for Escherichia coli. We tested the effects on the β-glucuronidase activity of E. coli W3110 of substances usually present in foods and several synthetic pharmaceutical compounds. Thirteen substances were tested: three carbohydrates, four flavonoids, five monosaccharide derivatives, and dimethyl sulphoxide. In a minimum medium without any other carbon source, glucose (0.1 mM), quercetin (0.1 mM), silymarin (10 mg/L), D-gluconic acid (0.01 mM), D-gluconic acid lactone (0.01 mM), isopropyl-β-D-thiogalacto pyranoside (1 mM), p-nitrophenyl β-D-glucuronide (1 mM), and DMSO (1 M) completely inhibited E. coli glucuronidase activity at the above concentrations. However, the following compounds stimulated E. coli glucuronidase activity within the ranges of concentrations shown: glucose (0.0001–0.01 mM), lactose and sucrose (>0.1 mM), D-saccharic acid 1,4 lactone (0.0001–0.1 mM), p-nitrophenyl β-D-glucuronide (0.001–0.01 mM) and DMSO (2–500 mM). In a rich culture medium that contained other carbon sources (lauryl tryptose broth) E. coli glucuronidase activity in the presence of the extra nutrients was unaffected by the test substances and therefore, under normal conditions in water or foods, they should not interfere with E. coli assays based on measurements of β-glucuronidase activity.