Method for improving accuracy of virus titration: standardization of plaque assay for Junin virus.

Titrating infective virus is one of the most important and common techniques in virology. However, after many years of widespread use, the parameters governing the accuracy of titration values are still not well understood. It was found that under conditions currently used for virus titration, only a small percentage of virus in the inoculum is adsorbed onto the cells and thereby detected in the titration assay. The objective of our work was to establish the conditions for a plaque assay which could estimate more accurately the titer of Junin virus. Two different stain methods were compared and several parameters governing plaque formation were studied. The volume of the inoculum appeared as the most important factor affecting observed titer. A linear relationship between the volume of inoculum and the reciprocal apparent titer allowed us to estimate an absolute titer by extrapolation. The approach described here is likely to be applicable to the more accurate estimation of the titer of a wide range of virus.