Fig. 5.

Relative fitness of resistant mutants in the presence and absence of the antibiotic. Forty resistant mutants isolated at the endpoint of the experiment competed with the susceptible ancestral strains in the presence (circles) and absence of the antibiotic (squares). The concentration of the antibiotic used in competition experiments was the same as that used during the selection experiments. Relative fitness is given as selection coefficients. Different colors represent different antibiotics. Eight independent competitions were performed in each case. The error bars represent a standard deviation. Two-tailed Student’s t-test was performed to test for statistically significant differences at P = 0.05. Black * indicates that relative fitness is statistically different from 0, both in the presence and absence of the antibiotic, while gray * indicates that relative fitness is statistically different from 0 only in the presence of the antibiotic.