Norman A. Clarke

Application of the “most probable number” method for estimating concentrations of animal viruses by the tissue culture technique

Abstract Justification for use of an MPN (most probable number) method for estimating concentration of Coxsackie B1 virus in monkey kidney tissue culture tubes was demonstrated by comparison of dosage-response data with a theoretical MPN curve based on one-particle infection and by variance analysis of 24 replicate MPN determinations. This method yields units comparable to plaque counts or plaque-forming units and affords unbiased estimates even when data do not bracket the 50% response dilution. It provides a means of testing for conformity to the one-particle infection theory and gives usable results from one dilution if both positive and negative tubes are present. For these reasons it is preferred to conventional LD 50 methods for virus quantitation where the dilution response data are known to follow the one-particle infection curve. A table of 5-tube, 4-fold dilution series and an approximation equation are presented for conversion of data to “most probable number of cytopathogenic units” (MPNCU).