FIG. 7.

Bacteriostatic activity of fluoroquinolones with wild-type (wt) and quinolone-resistant gyrA mutants of E. coli. Isogenic strains of E. coli containing alleles of gyrA or gyrB were incubated overnight in LB broth containing the indicated fluoroquinolone to determine the MIC₉₉. The ratio of the mutant to the wild-type MIC₉₉ was determined for each mutant. The GyrA amino acid substitutions, arranged from left to right, were A51V, A67S, G81C, D82A, S83L, S83W, A84P, D87N, D87Y, and A106H; to the right are GyrB variants K447E and D426N (the strain numbers are listed in Table 1). The MICs of compounds D, K, F, and I for wild-type cells were 0.1, 0.02, 0.1, and 0.05 μg/ml, respectively. Similar results were obtained in a replicate experiment.