This method represents a quantitative measure of infectious virus particles within a sample. It involves infecting a susceptible cell monolayer with a diluted virus suspension, allowing the virus to adsorb and infect cells. After an incubation period, a visible area of cell lysis, or plaque, forms, indicating localized viral infection. The number of these plaques is then counted, and taking into account the dilution factor, the concentration of infectious virus is determined. As an example, if a 10^-5 dilution yields 50 plaques, the original sample contains 5.0 x 10^6 infectious units per unit volume.
This process is crucial for various applications in virology, including determining viral titer for experiments, assessing the efficacy of antiviral drugs, and characterizing viral mutations that affect infectivity. Its reliability and relative simplicity have made it a cornerstone technique in virological research for decades, providing a fundamental measure of viral concentration applicable across a wide range of viruses and cell types.
