Single mutations decrease drug susceptibility and increase fitness.

aGenotype; All strains are isogenic to MG1655 and carry only the mutations shown.
bMIC for ciprofloxacin (µg/ml).
cFitness; Mean fitness per generation (relative to wild-type). SD, standard deviation (within parentheses) measured in pair wise competition against the isogenic wild-type.
dP; Significance of fitness difference between the strains in each pair, (Students t-test, two-tailed P-value).
eN; Number of independent competition experiments on which the fitness value is based.