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. 2009 Oct 5;54(1):149–156. doi: 10.1128/AAC.01035-09

FIG. 3.

FIG. 3.

Effect of defects in DNA metabolism on the induction of quinolone-resistant mutants by nalidixic acid. (A) Genes controlling the SOS response. E. coli strains containing noninducible lexA3 (strain KD1437; 2.5 × 107 CFU; filled triangles), inactive recA56 (strain KD79; 2.5 × 107 CFU; open circles), or neither mutation (strain DM4100; 2.5 × 107 CFU; filled circles) were applied to agar containing nalidixic acid at three times the MIC99. At the indicated times, the cumulative number of colonies was recorded and is expressed as a fraction of the number of input cells. (B) Effect of ung mutator. E. coli strains containing a deficiency of ung (strain KD2928; 1.2 × 108 CFU; open circles) or the wild-type ung allele (strain DM4100; 1.1 × 108 CFU filled circles) were applied to agar containing 6 μg/ml nalidixic acid (two times the MIC), and the colonies were counted at the indicated times. Replicate experiments with a variety of nalidixic acid concentrations (1.5 to 3 times the MIC99) gave similar results for both panels.