Comparison of two methods of virus detection by immunosorbent electron microscopy (ISEM) using protein A

The efficiency of two methods of immunosorbent electron microscopy has been compared. The first method consists in trapping virus particles by means of Staphylococcus aureus cells coated with a layer of viral antibodies; the second method consists in trapping virus particles o electron microscope grids coated with specific antibody. A suspension containing 107 antibody-coated bacteria trapped the total number of virions present in 1 ml of a 500 ng/ml virus preparation; the cells were then fully saturated with virions, and approximately 100 virions (of 30 nm diameter) were visible at the periphery of each cell. When 107 cells/ml were used the minimum virus concentration needed to see one virion at the cell periphery was 5 ng/ml. Antibody-coated grids allowed for the detection of approximately the same quantity of virus, but the data obtained with the method were more reproducible and suitable for quantitation.