FIG 4.
Ferric citrate uptake is an in vitro fitness factor in the absence of enterobactin. In vitro fitness of strains or conditions was determined in ex vivo pooled human urine. All strains were inoculated in a 1:1 ratio and grown for 24 h at 37°C with aeration, and their log10 competitive index (CI) was determined. A log10 CI of <0 indicates the first listed strain was outcompeted by the second. (A) The ΔentB mutant expressing an empty vector (ΔentB eV) and the ΔfecA/ΔentB double mutant with the fec operon complemented in trans (ΔfecA+fec/ΔentB) were competed in urine supplemented with 0.5% arabinose and ampicillin (100 μg/mL). (B) WT HM7 was competed with the ΔfecA mutant, and the urine was supplemented with either recombinant human lipocalin (Lcn2) or an equal volume of vehicle (25% glycerol). Red asterisks indicate a significant competitive disadvantage, determined by one-sample t test: *, P < 0.05; **, P < 0.005. Black asterisks compare log10 CIs between indicated strains or conditions using an unpaired t test: *, P < 0.05; **, P < 0.005. Bars indicate the mean; error bars are ±SEM. Each dot represents an independent experiment.