FIG. 2.

Competitions in batch cultures. The relative fitness of the ΔI-VII mutants compared to E. coli 536 WT in LB (dashed lines) and urine (solid lines) over 10 cycles (i.e., 100 generations) of growth in batch cultures was determined as described in Materials and Methods. The competition opposing the ΔI strain to the ΔI::Cm strain was used as a control for the cost of the chloramphenicol resistance cassette present in the ΔI-VII mutants. Error bars represent the standard error of the mean of at least three experiments. ΔI-to-VII mutants significantly outcompeted the WT in each medium after about 100 generations (*, P < 0.05, Wilcoxon signed-rank test). R, antibiotic-resistant strain; S, antibiotic-sensitive strain.