Strain Differences of Toxoplasma gondii

Abstract

The RH strain, virulent for mice, invades 5.1 times as many cells and multiplies 2.25 times as fast as the relatively avirulent 113 CE strain. In monkey kidney tissue culture tubes 200,000 RH toxoplasmas destroy the cultures in 4 days, 1,000,000 113 CE organisms, which give comparable initial levels of cellular invasion, cause slow and erratic lysis of the cultures. Organisms of both strains inoculated into tubes in a roller drum invade only about 1/4 as many cells as those inoculated into tubes in stationary racks, indicating that a finite time is required for cellular invasion by the organisms. Cultures infected with the 113 CE strain and 721 strain, kept 21 days after inoculation, often showed essentially normal cell sheets with only a few live organisms remaining. Cellular regeneration seemed to balance cell lysis and no clear-cut abnormalities were grossly visible in the cell sheet.