Murine lung infection model studies with KR2107 and its isogenic fim and/or fim2 mutants. (A) Comparison of the ability of KR2107 and its isogenic mutants to infect the lungs as assessed by two head-to-head competition assays. A mixture containing an equal ratio of each competing strain was inoculated intranasally into five mice. The competitive index (CI) is the ratio of the number of fim2-positive to fim2-negative bacteria recovered from infected organs divided by the equivalent ratio as present in the intranasal inoculum. (B) Differential CFU counts for each of the competing strains in the liver at 30 h post-inoculation. (C) Liver CFU counts obtained in the five mice used for the competition assay between KR2107 and its isogenic fim2 mutant. In A and B, 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.