FACS-based Whole Cell ELISA Assay

The whole cell enzyme‑linked immunosorbent assay (whole cell ELISA) is an immunological binding assay used to measure serum antibody responses directed against surface antigens expressed on intact bacterial cells. The assay involves live bacteria, usually grown until the mid-exponential phase, incubated with serially diluted sera. Antibodies can bind to native surface epitopes on live bacteria prior to fixation, thereby avoiding alterations that may mask certain antigens or reduce assay sensitivity. Bound antibodies are detected using fluorescently labeled secondary antibodies and analysed by flow cytometry, with signal intensity directly proportional to the level of antibody binding. In VisMederi, the assay is primarily used to assess humoral immune responses against Neisseria gonorrhoeae but can be readily adapted to evaluate immune responses against other bacterial pathogens.