FIG 2.

MgrB⁻ has a fitness defect in gut colonization that is rescued by antibiotic treatment. (A) Fecal shedding of infected mice. Mice were infected orally with either WT, MgrB⁻, or MgrB⁺ K. pneumoniae, and feces was collected on the days indicated (n ≥ 10 for each group). Each point indicates a single mouse on a given day, the bars indicate the median shedding, and the dotted line indicates the limit of detection; significance symbols shown are between WT and MgrB⁻. Kruskal-Wallis test followed by Dunn’s test of multiple comparisons was performed at each time point for analysis; WT and MgrB⁺ were not significantly different. (B) Competitive index (CI) of infected mice. Mice were infected orally with a 1:1 mixture of the WT and MgrB⁻ mutant, with feces collected on the days indicated (n ≥ 10). The CI was determined as described in Materials and Methods. Each symbol represents the log₁₀ CI value from an individual mouse on a given day, with a bar indicating the median value. The dashed line indicates a competitive index of 1 or a 1:1 ratio of WT to mutant. (C) Colonization density of the colon, cecum, ileum, and oropharynx represented as log₁₀ CI values from an individual mouse at the end of the study. For both B and C, statistical differences were determined by Wilcoxon signed-rank test. (D) K. pneumoniae fecal shedding from mice treated with antibiotic (AB). Mice were infected orally with either WT or MgrB⁻, and 2 days postinfection, they were given a dose of 5 mg of streptomycin via oral gavage. The shaded gray area indicates the duration of antibiotic treatment. Shown are the means and standard error of the means for both WT (n = 6) and MgrB⁻ (n = 6) infected mice, the black dotted line indicates the limit of detection, and the gray dotted line indicates the super shedder threshold. Statistical differences were calculated using a Mann-Whitney U test at each time point. *, P < 0.05; **, P < 0.01; ***, P < 0.001.