Viability and infectivity analysis of <i>Toxoplasma gondii</i> under axenic conditions

Abstract

AIMS: To investigate the infectivity and viability of the tachyzoite form of Toxoplasma gondii maintained in axenic medium. METHODS: Tachyzoites of Toxoplasma gondii isolated from infected mice were suspended in phosphate-buffered saline pH 7.2 or phosphate-buffered saline pH 7.2 plus 10% or 20% foetal calf serum, and incubated for 24 and for 48 hours at 37ºC. Afterwards the parasites were: (i) incubated with propidium iodide and analysed by flow cytometry, using the fluorescence-activated cell sorting (FACS) system; (ii) injected in mice to check the parasite viability in axenic conditions and, (iii) added to mouse embryonic fibroblasts to investigate their infectivity and ability to intracellular development. RESULTS: Analysis by flow cytometry showed that Toxoplasma gondii tachyzoites maintained in phosphate-buffered saline supplemented with 20% foetal calf serum displayed high cellular viability. The parasites kept their infectivity in both the in vivo and the in vitro systems, respectively demonstrated by their ability to replicate in mice and to form rosettes in mouse embryonic fibroblasts. CONCLUSIONS: Our data open new perspectives for the study of different aspects of Toxoplasma gondii cell biology, including nutrition mechanisms, in vitro drug trials, or cellular and molecular studies to be performed directly on the parasite.