Rapid Identification and Quantitation of Cells Infected by Recombinant Herpesvirus (Pseudorabies Virus) Using A Fluorescence-Based β-Galactosidase Assay and Flow-Cytometry

We recently described construction and use of a β-galactosidase expression cassette in isolating recombinant pseudorabies virus (PrV) mutants (Mettenleiter and Rauh, 1990). We report here the identification and exact quantitation of cells infected by these mutants using an assay based on the reaction of intracellular β-galactosidase expressed during infection by the recombinant viruses with the fluorogenic substrate fluorescein di-β-D-galactopyranoside (FDG) followed by detection of positive cells in flow cytometry (FACS-Gal assay; Nolan et al., 1988). The detection method is fast, sensitive, and reliable, and yields quantitative results on single cell basis.