Use of Protein A in the Serum‐in‐Agar Diffusion Method in Immune Electron Microscopy for Detection of Virus Particles in Cell Culture

Furui, Sataro

A modified technique using protein A in the serum‐in‐agar (SIA) method for immune electron microscopy (IEM) was presented. Grids coated with staphylococcal protein A were floated on samples mounted on agar containing 2% antiserum and incubated at 37 C, for 60 min. After washing and staining, the grids were observed in an electron microscope. The effects of protein A on virus detection were evaluated using poliovirus and bovine rotavirus infected cell culture fluids. The results showed that the technique using protein A (PA‐SIA) had at least 10‐fold higher sensitivity for virus detection than the original SIA. The optimal concentration of protein A was 1 to 10 μg/ml for coating the grids to trap virus particles. The PA‐SIA method was also compared with immunosorbent electron microscopy (ISEM). The former showed higher or at least the same sensitivity and some advantages in detecting antigen‐antibody reaction than the latter method. These results indicate that our PA‐SIA method may be superior to other IEM techniques presented previously for the detection and identification of viruses.