FIG. 1.
Screen for mutants with low levels of persistence. (A) Frequency of amdinocillin-resistant mutants in E. coli K-12 BW25113. Stationary-phase culture in LB medium was serially diluted in twofold steps and plated onto LB agar supplemented with 4 μg/ml amdinocillin. Samples from each dilution were also removed for determination of the colony counts. The frequency was 5 × 10−5 on the basis of the initial cell counts and the number of amdinocillin-resistant mutants arising on LB agar supplemented with amdinocillin. (B) Survival of E. coli BW25113 stationary-phase cells challenged with ofloxacin. Stationary-phase cultures grown in MOPS minimal medium were treated with ofloxacin at the indicated concentrations for 6 h and plated for determination of the colony counts. The experiment was performed in triplicate, and error bars represent standard deviations. (C) Survival of strains from the Keio collection. Mutant strains cultured in MOPS minimal medium were treated with ofloxacin for 6 h, and samples were plated on LB agar supplemented with 4 μg/ml amdinocillin and 20 mM MgSO4. Two hits are circled.