FIGURE 6.

FH6-7/IgG binds to and increases serum killing of a large majority of M. catarrhalis clinical isolates. (A) 21 clinical isolates and the laboratory strain RH4 were tested for FH6-7/IgG binding by flow cytometry. In the absence of FH6-7/IgG, bacteria incubated with detection antibody had a similar gMFI for all isolates (average 151, standard deviation 45). (B–D) Twelve clinical isolates were treated with 50 μg/ml of FH6-7/IgG or PBS, at the same time as 15% NHS, and their survival after 30 min was assessed by plating bacteria and counting remaining colony forming-units (CFU). The remaining nine isolates were not included because their survival in serum in the absence of fusion protein was less than 5%. (B) UspA2 NTER2A strains, (C) UspA2 NTER2B strains, (D) UspA2H strains. Mean (±SD) from three (A–C) or four (D) independent experiments are shown. Statistical significance of differences was calculated using two-way ANOVA with Holm–Sidak’s post-test; *p < 0.05; **p < 0.01; ***p < 0.001.