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.