Continual cultivation of Toxoplasma gondii on HeLa cells

Continual cultivation of Toxoplasma gondii in monolayers of HeLa cells has been performed for 6 years. The toxoplasmas were then used for serial cultivation experiments. While searching for optimal conditions for toxoplasma inoculation it was found that infected HeLa cells which were scraped off the glass were a more suitable inoculum than those released by trypsinization. The optimal dose was one zoite per 12 host cells, medium level height at adsorption 2 mm and adsorption time 90 min at 37 degrees C. The concentration of sodium bicarbonate ranging from 8.7 to 26.1 mM had no effect on the multiplication of toxoplasmas. In serial passages in Roux bottles, when the medium was changed every 2-3 days, the average yield of toxoplasmas was 6.2 X 10(6) per ml of medium (after the second change of medium, i.e., 7 days after inoculation). The toxoplasmas obtained in serial passages were suitable for purification studies, for preparation of small amounts of antigens and as an inoculum for suspension cultures.