Serum Bactericidal Assay with Fluorescence Readout (FL-SBA)

The Fluorescence-SBA (L‑SBA) follows the same principles as the conventional serum bactericidal assay (SBA), but it measures antibody-mediated bactericidal activity by quantifying fluorescence as an indirect indicator of bacterial survival. This is achieved using a metabolic readout or genetically modified bacteria that produce a fluorescent signal. In FL-SBA the level of fluorescence detected is directly proportional to the number of bacteria present in the assay wells, which is inversely proportional to the level of functional antibodies present in the serum. Therefore, serum bactericidal titer obtained by the fluorescence readout method strongly correlates with the data obtained by the conventional agar plate-based assay. The fluorescence readout, similarly, to the luminescence readout, overcomes the major limitations of the conventional SBA by enabling bactericidal titers to be calculated directly in a microplate-based format; for this reason, it can be used as a high-throughput functional assay to evaluate vaccine immunogenicity. When appropriately validated and qualified this approach provides a rapid, sensitive, and high‑throughput alternative to conventional SBA as valuable evidence to support the clinical development and regulatory approval of bacterial vaccines. The pathogens most commonly evaluated using this method at VisMederi are Neisseria gonorrhoeae and Borrelia spp.