INTERFERENCE BY CARBOHYDRATE SUBSTRATES, FLAVONOIDS, AND MONOSACCHARIDE DERIVATIVES ON BACTERIAL BETA-D-GLUCURONIDASE ASSAYS

Most commercially available test kits for water and foodstuffs use bet a-galactosidase activity for coliforms and beta-glucuronidase activity for Escherichia coli. We tested the effects on the beta-glucuronidase activity of E. coli W3110 of substances usually present in foods and several synthetic pharmaceutical compounds. Thirteen substances were t ested: three carbohydrates, four flavonoids, five monosaccharide deriv atives, 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), iso propyl-beta-D-thiogalacto pyranoside (1 mM), p-nitrophenyl beta-D-gluc uronide (1 mM), and DMSO (1 M) completely inhibited E. coli glucuronid ase activity at the above concentrations. However, the following compo unds stimulated E. coli glucuronidase activity within the ranges of co ncentrations 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 bet a-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 wa s unaffected by the test substances and therefore, under normal condit ions in water or foods, they should not interfere with E. coli assays based on measurements of beta-glucuronidase activity.