FIG. 1.

Patchwork structure of bacterial populations selected at different antibiotic concentrations. The different bacterial populations that can be obtained upon selection with different concentrations of the same antibiotic are shown. Six different phenotypes, each one corresponding to mutations either in different loci or in different positions in the same locus, that render different MICs are indicated. The rectangles show the compositions of the bacterial populations selected with the antibiotic concentration fixed by the arrow at the bottom. The black box at the bottom of all rectangles contains the same amount of bacterial cells in all populations. Note that for any population maximum selection is obtained at selective antibiotic concentrations close to the MIC for the population.