Quantitative Giemsa cell monolayer viability assay

Cell viability is routinely quantified through pricey assays measuring ephemeral signals resulting from specimen destruction, making simultaneous visual assessment often challenging. To balance cell viability visualization, affordability and quantitative results, the well-established Giemsa standard plaque assay (G-SPA), commonly used to stain infected cell monolayers for viral titer estimation, has been further developed here into a quantitative viability assay. Cell monolayers treated with serial dilutions of solvents, drugs and virus stained with Giemsa as for G-SPA, provide a visual staining of cell viability correlating with a signal intensity that can be measured with a plate reader with negligible well-to-well signal crosstalk. Moreover, results are didactic as the staining can be seen in the plates with the naked eye, physically stored or archived, and used to estimate cell cytotoxicity and cytopathic effect quantitatively. The Giemsa staining can also be dissolved and reversed with DMSO or methanol, allowing for signal uniformization, off-plate quantification and even re-staining.