Figure 1.

Experimental design of the study: adaptation of E. coli K12 to three antibiotics following four adaptation protocols with different selection strengths. The four selection systems are named “gradient,” “100% increment,” “50% increment,” and “25% increment.” In the gradient approach, cells were inoculated into a 2-fold, 10-step drug gradient and cells growing in the highest concentration were used for inoculation of a fresh gradient. In the increment approaches the drug concentration was raised with every transfer either by 100, 50, or 25%. The wild type minimal inhibitory concentration (MIC) was reached on the fourth day of the experiment for all increment lineages.