Figure 2.

Serum bactericidal assay showing the contribution of immunoglobulin G and CRP to the survival of phase variants in the expression of ChoP in NHS. ChoP⁺ (solid bar) or ChoP⁻ (hatched bar) variants of nontypable strain H233 were grown to midlog phase and treated for 60 min in 10% pooled NHS. The percentage of survival is the number of CFUs remaining compared to controls in which complement activity was inactivated. In A, determinations were carried out in the presence of untreated NHS (lane 1), NHS depleted of IgG (lane 2), NHS depleted of IgG with the addition of 0.05 M Mg²⁺ EGTA (lane 3), NHS depleted of IgG and CRP (lane 4), NHS depleted of CRP alone (lane 5), or NHS depleted of CRP with the addition of purified human CRP (5 μg/ml) (lane 6). In B, before use in the bactericidal assay with CRP-depleted NHS, phase variants were pretreated with purified human CRP in the presence of EDTA (lane 7) or Ca²⁺ (lane 8). Values are the geometric mean of at least three determinations in duplicate ± SD.