Minimal Broth Davis w/o Dextrose is recommended for the isolation and characterization of nutritional mutants of Escherichia coli. A cell suspension of wild type Escherichia coli is irradiated and cultured on Minimal Agar and incubated at 35°C for 24hours. The isolated colonies are cultured in tubes of Minimal Broth Davis (M389) and Minimal Broth Davis without Dextrose(M390). After 24 hours incubation at 35°C growth in the Minimal Broth, Davis and absence of growth in the Minimal BrothDavis without Dextrose indicates a mutant.