Murine urinary tract infection model studies with KR2107 and its isogenic fim and/or fim2 mutants. (A) Comparison of the urovirulence of KR2107 and its isogenic mutants as assessed by two head-to-head competition assays. A mixture containing approximately equal numbers of each competing strain was inoculated into the bladders of six mice. The competitive index (CI) is the ratio of the number of fim2-positive to fim2-negative bacteria recovered from urine or bladder divided by the equivalent ratio as present in the infecting inoculum. (B) Differential CFU counts for each of the competing strains in the left and right kidneys at 3 days post-inoculation. In both of the above analyses horizontal bars represent the median, with data points for each mouse as indicated. The lower limit of detection is represented by the dotted line. P values were calculated using the Mann–Whitney U test.