Protein A-Mediated Binding ofStaphylococcusspp. to Antibodies in Flow Cytometric Assays and Reduction of This Binding by Using Fc Receptor Blocking Reagent

This study characterizes a widespread but little-studied problem associated with the antibody-based detection of microbes—the Staphylococcus protein A (SpA)-mediated binding of IgG antibodies—and offers a solution: the use of commercial FcR blocking reagent. A common source of false-positive signals in the detection of microbes in clinical, food, or environmental samples can be eliminated by applying this study’s findings. Using flow cytometry, the authors demonstrate the extent of heterogeneity in a culture’s SpA-mediated binding of antibodies and that the degree of SpA-mediated antibody binding is strain, growth phase, and food matrix dependent and influenced by simulated food processing treatments and cell adherence. In addition, our studies of SpA-mediated binding of Staphylococcus spp. to antibodies against other bacterial species produced a very nuanced picture, leading us to recommend testing against multiple strains of S. aureus and S. hyicus of all antibodies to be incorporated into any immunoassay designed to detect a non- Staphylococcus spp.