Which technique is employed for the direct visualization of the virus in cell cultures?

The technique employed for the direct visualization of viruses in cell cultures is immunofluorescence. This method utilizes antibodies that are labeled with a fluorescent dye, allowing for specific binding to viral antigens in infected cells. When exposed to ultraviolet light, the bound antibodies emit fluorescence, which can be observed and documented under a fluorescence microscope. This technique is particularly valuable because it provides a direct way to identify and visualize viruses within the context of infected cells, facilitating the study of viral infections.

In contrast, staining typically refers to various laboratory techniques that enhance the contrast of cells or tissues but may not specifically target viral particles or antigens. While the cytopathic effect describes the observable changes in host cells induced by viral infection, it does not provide direct visualization of the virus itself. Lastly, enzyme-linked immunosorbent assay (ELISA) is primarily a quantitative technique used to detect the presence of viral proteins or antibodies in a sample but does not allow for direct visualization in cell cultures. Thus, immunofluorescence is the clear choice for directly visualizing viruses.