Serotyping of human astrovirus strains by immunogold staining electron microscopy

Human astrovirus strains were propagated in CaCo-2 cell cultures, and virus multiplication was demonstrated by immunosorbent electron microscopy (ISEM). Serotyping of the virus strains was carried out in cell culture fluids or directly in faecal extracts by an indirect immunogold staining (IGS) electron microscopy technique, using specific rabbit antisera against astrovirus types 1-6 as primary antibodies and goat anti-rabbit IgG gold conjugate as secondary antibody. Thirty-seven astrovirus strains were examined, of which 26 grew in the cell cultures in several passages. IGS of the cell-derived viruses showed that 16, 3, 3, and 4 of the strains were types 1, 2, 3, and 4 respectively. Types 5 and 6 were not demonstrated. Eleven strains did not grow in cell cultures, and attempts to serotype these strains by IGS directly in the faecal extracts were unsuccessful, except for one strain which was found to be type 1. The results indicate that IGS may be a specific and suitable method for serotyping astroviruses grown in cell cultures.