Virulent strains of Toxoplasma gondii superinfect genetically resistant hosts.

CEP hxgprt- chronically infected C57BL/10, C57BL/10.A, and A/J mice were given a secondary infection with the indicated atypical T. gondii strain; then, 35–45 days after secondary infection, brains from surviving mice were homogenized in PBS and used to inoculate HFF monolayers. The resultant parasite cultures were then tested for the presence of the secondary infection strain; numerator = number of mice tested positive for secondary infection strain in the brain; denominator = number of mice that exhibited parasite growth in the HFF monolayer prior to drug selection. 1Parasite growth was observed in mycophenolic acid / xanthine medium, which selects for parasites encoding a functional HXGPRT gene (i.e. the challenging atypical strains) and kills the primary infection CEP hxgprt- strain. (XLSX)