FIG 5 .

Relative fitness (A and B) and fold increase in MIC (C and D) of either mutant allelic constructs (dark gray) or evolved isolates (light gray) for constant (A and C) and fluctuating (B and D) treatments. The legend provides details on the mutations in the allelic constructs. Error bars represent an SE of ±1. MIC values were calculated as medians of results from four trials. Mean relative fitness was 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.