Figure 4.

(A) reciprocal, variable trade-off between fitness and susceptibility evident in natural E. coli isolates. Fitter strains are more susceptible to antibiotics; for example, ECOR29 is the least fit but the most resistant. Conversely, ECOR56 is the fittest, but also the most susceptible. The growth of the E. coli ECOR strain set on plates containing 3 μg/mL chloramphenicol (Cm) was determined as in [50]. Fitness measured as a selection co-efficient (s) was obtained after 48 h of growth in competition with a reference strain (MG1655) in nutrient-limited chemostats from data in [50]. Mutational shifts in SPANC setting are shown by arrows for strains evolved after nutrient limitation (ECOR5E) or growth in the presence of antibiotic (ECOR59E); (B) Changes in the zone of inhibition of ECOR and derived strains were determined using disks with 8 μg/mL Cm.