Fig. 7.

Contribution of the exponential growth rate and growth yield (stationary phase population density) to mutant fitness. Relative exponential growth rate and relative growth yield (with respect to the susceptible ancestral strain) were calculated for the resistant mutants in the (A) absence and (B) presence of the antibiotic. The wild-type values were set as 1 in each case and are shown as dotted lines. (C) The ratios between these measurements in the presence and absence of the antibiotic were calculated to determine the contribution of these fitness components to the increase in fitness. A value different from 1 would represent a measurable contribution of either an increased exponential growth rate or growth yield to the increased fitness. Error bars along both the x-axis and y-axis represent standard deviations. Different shapes represent antibiotic concentrations where selection for specific resistant mutants was observed, while different colors represent different antibiotics.