Validation of colorimetric assay to detect complement-mediated antibody-dependent bactericidal activity against serogroups B and C Neisseria meningitidis

Colorimetric serum bactericidal assay (cSBA), based on the addition of glucose and a pH indicator to the culture medium after the bactericidal reaction, was validated. The precision measured as repeatability, intermediated precision, and reproducibility was determined as a percentage in titer coincidence between replicas >/=50. Moreover the use of the freeze-dried complement was evaluated in comparison to the traditionally stored by freezing. The results were the following: precision: titer +/-1 two-fold dilution (except for the highly positive serum against serogroup B, where there was titer +/-2 dilutions) percentage in titer coincidence: >/=50. The known titer or +/-1 two-fold dilution was found in the sera titrated with the complement either frozen or freeze-dried. Concluding, cSBA showed to be highly precise, allowing also the use of freeze-dried complement which is another important advantage for this kind of assay.