Fig 2.

N. gonorrhoeae serum bactericidal assay. (A) N. gonorrhoeae strain FA1090 (10³ CFU) was incubated with the indicated concentration of 6B4 or HBSS buffer, followed by the addition of the indicated concentration of Ig-depleted normal human serum. Bacterial CFU from 20 µL of the incubation medium were enumerated after overnight growth on GCB agar. (B) Bacteria killed were expressed as a percentage of the buffer (HBSS) control and graphed relative to the concentration of 6B4 in 2% NHS (solid circles). The dotted lines indicate the extrapolation to the 6B4 concentration that yields 50% bacterial killing. The SBA titer, or the lowest concentration that yielded ≥50% killing, was calculated as 0.4 µg/mL (green). Five percent heat-inactivated (HI) NHS, the highest concentration of NHS that was tested, served as a negative control (open circles). Bars indicate the mean ± SD of three independent experiments, with each biological replicate as one data point.