Toxoplasma gondii: a simple method for titration of infectivity with monolayer cells

A simple method for assessing the infectivity of Toxoplasma gondii using primary cultured monolayer cells has been devised. Statistic analysis important for interpreting the results of such experimentation was made. In this method, the number of intracellular toxoplasmas and the percentage of confluency of the monolayer were measured. The latter value was used for conversion of the number of intracellular toxoplasmas per unit area to the percentage of infective toxoplasmas. A linear dose-response relationship between the number of intracellular toxoplasmas per unit area and that of toxoplasmas inoculated was demonstrated with primary cell monolayers from the lungs of two-day old inbred golden hamsters and the kidneys of newborn mice and newborn Wistar Imamichi strain rats. On the average, 37% of the toxoplasma organisms harvested from the peritoneal exudate of mice on the third or fourth day of infection were found to be infective. This value compares very favorably with the value 40% reported previously.