FIG 4 .

The fold increase in MIC (A, C, and E) and relative fitness effect (B, D, and F) of individual mutations that arose during the course of our selection experiment in nfxB (A and B), gyrB (C and D), and gyrA (E and F). Error bars represent an SE of ±1. MIC values were calculated as medians of results from four trials. Mean relative fitness levels were measured in the absence of antibiotic via direct competitions with a lacZ-marked ancestral isolate (PA14) using 1 to 10 replicate measures for each allelic construct. A relative fitness value of less than 1 indicates a cost of resistance in the absence of the antibiotic.