FIG. 2.
Virulence of wild-type and phoP mutant strains. Various doses of meningococci were administered i.p. with human holotransferrin (10 mg) to groups of five Harlan-NIH inbred female mice. The day after infection, mice that had not already been humanely killed were boosted i.p. with human holotransferrin (10 mg). (a) Number of surviving mice at different times postinfection. (b) Health scores for surviving mice. Healthy mice were given an arbitrary health score of 5. The following observable symptoms resulted in cumulative deductions in health score: ruffled fur, −1, eyes shut, −1; ruffled fur and eyes shut, −2; immobile, −4. Health was regularly monitored, with any signs of ill health being indicative of lethal infection and scored as above; the mice were humanely killed when immobile. Solid lines, wild type; dashed lines, phoP mutant. The number of bacterial cells inoculated into the mice was 6 × 107 (circles), 6 × 106 (diamonds), or 6 × 105 (squares).