Effect of complement inhibitors on survival of 4 N meningitidis strains in whole blood from vaccinated adult subjects. Geometric mean CFU per milliliter (95% confidence interval) after incubation of meningococci for 3 hours. (A-B) Data from 12 subjects tested against serogroup B strain H44/65 and serogroup C strain 4243, respectively. (C-D) Serogroup B strains Ohio University and Quebec tested with blood from 5 subjects immunized with MenB-4C. Irrespective of the strain tested, eculizumab blocked killing of bacteria and the geometric mean CFU per milliliter increased significantly at 3 hours compared with time 0 (P < .0001). In contrast, in the presence of the complement factor D inhibitor ACH-4471, the geometric mean CFU per milliliter of blood decreased at 3 hours compared with time 0 (P < .005 for strains H44/76, 4243, and Quebec; P = .13 for Ohio University). The P values for comparisons between the respective geometric mean CFUs per milliliter at 3 hours for the different treatment groups for each strain are provided in “Results.”