The ability to measure the opsonic activity of antibody may be critical in choosing among potential therapeutic candidates. It has been shown in numerous studies that the ability of antibody to mediate clearance of bacterial organisms in animal models and in humans is related to its in vitro opsonic activity and not solely to its antigen binding activity. We have developed a rapid and robot adaptable opsonophagocytosis assay for Staphylococci based on bioluminescence produced by bacteria transfected with the luciferase operon. Opsonophagocytosis is measured by the loss of bioluminescence as bacteria are opsonized by phagocytes and killed. Pagibaximab is a humanized monoclonal anti-lipoteichoic acid (LTA) antibody opsonic for S. epidermidis and S. aureus, which we used to develop this rapid bioluminescence assay.