Fig 3. Assaying for hypermutation using ß-glucuronidase assay on MUG Selective agar.

MUG selective agar was formulated using methyl-umbelliferyl-glucuronide (MUG) as stated in Materials and Methods. STEC Popeye-1 was treated with zidovudine as indicated for 3 h, followed by serial dilutions and plating on MUG Selective agar as well as on plain LB plates to determine total counts. Panel A, plate of untreated Popeye-1 on MUG agar, showing that although faint colonies are visible they do not fluoresce. Panel B, a heavy inoculum of zidovudine-treated Popeye-1 formed a lawn of growth, within which several brightly fluorescent colonies are visible. Panel C, dose-response of zidovudine on the frequency of glucuronidase-positive colonies, in the absence and presence of zinc.