Nutrient Agar with MUG is used for detecting and enumerating Escherichia coli in water.
SUMMARY AND EXPLANATION
Escherichia coli is a member of the fecal coliform group of bacteria. The presence of E. coli is indicative of fecal contamination. Feng and Hartman developed a rapid assay for E. coli by incorporating 4-methylumbelliferyl-β-D-glucuronide (MUG) at a final concentration of 100 μg/mL into Lauryl Tryptose Broth. Nutrient Agar is similarly modified with the addition of MUG. Rapid quantitation and verification may be achieved with the membrane filtration procedure by transferring the membrane from a total-coliform or fecal coliform positive sample to a Nutrient Agar substrate containing 4-methylumbelliferyl-β-D-glucuronide (MUG).
Mates and Shaffer used the membrane filter-Endo Agar method, followed by incubation on Nutrient Agar with MUG, to detect and enumerate E. coli within 4 hours of membrane transfer. E. coli was recovered at a rate of 98% with no false-positive results.
Nutrient Agar with MUG is prepared according to the formula specified by the U.S. Environmental Protection Agency and published in Standard Methods for the Examination of Water and Wastewater.
Beef extract and peptone are sources of nitrogen, vitamins, carbon and amino acids. Agar is the solidifying agent. The substrate, MUG (4-methylumbelliferyl-β-D-glucuronide), produces a blue fluorescence when hydrolyzed by the enzyme β-glucuronidase, which is produced by most E. coli.