Fig. 4

MIC values over time in resistant strains exposed to a second antibiotic. Plots show MIC (ug/ml) of the first de novo acquired resistance, indicated on the X-axes, when exposed to amoxicillin (amx, a-c), enrofloxacin (enro, d-f), kanamycin (kan, g-i), or tetracycline (tet, j-l). The dotted black lines indicate the MICs for wild-type E. coli MG1655. Different lines in each plot indicate the different replicates. The percentage of residual mutations was determined by dividing the number of original mutations still present at the end of the experiment by the number of mutations observed in the beginning and multiplying this number by 100. The percentages are indicated in the plots using colors based on the gradient shown on the right