Comparison of two serum bactericidal assays for Neisseria gonorrhoeae

Pooled normal human serum killing of 14 strains of Neisseria gonorrhoeae was assessed by dilution plate and microtiter methods. In both assays, the strains presented a spectrum of sensitivity to the serum. In the dilution plate assay, results with two different concentrations of human serum were similar for most, but not all of the strains tested. When data for all of the strains were compared, no correlation was found between the dilution plate and microtiter bactericidal assays. Finally, we found that the bactericidal capacities of intact and complement-depleted human sera were very similar when assessed by microtiter methods, suggesting a non-complement-mediated serum killing mechanism.