Development and Application of Different Methods for the Detection of Toxoplasma gondii in Water

Abstract

Two methods, centrifugation and flocculation, were evaluated to determine their efficiencies of recovery of Toxoplasma gondii oocysts from contaminated water samples. Demineralized and tap water replicates were inoculated with high numbers of sporulated or unsporulated T. gondii oocysts (1 × 10 ⁵ and 1 × 10 ⁴ oocysts). The strain, age, and concentration of the seeded oocysts were recorded. Oocysts were recovered either by centrifugation of the contaminated samples at various g values or by flocculation with two coagulants, Fe ₂ (SO ₄ ) ₃ and Al ₂ (SO ₄ ) ₃ . The recovery rates were determined with the final pellets by phase-contrast microscopy. Sporulated oocysts were recovered more effectively by flocculation with Al ₂ (SO ₄ ) ₃ (96.5% ± 21.7%) than by flocculation with Fe ₂ (SO ₄ ) ₃ (93.1% ± 8.1%) or by centrifugation at 2,073 × g (82.5% ± 6.8%). For the unsporulated oocysts, flocculation with Fe ₂ (SO ₄ ) ₃ was more successful (100.3% ± 26.9%) than flocculation with Al ₂ (SO ₄ ) ₃ (90.4% ± 19.1%) or centrifugation at 2,565 × g (97.2% ± 12.5%). The infectivity of the sporulated oocysts recovered by centrifugation was confirmed by seroconversion of all inoculated mice 77 days postinfection. These data suggest that sporulated Toxoplasma oocysts purified by methods commonly used for waterborne pathogens retain their infectivity after mechanical treatment and are able to induce infections in mammals. This is the first step in developing a systematic approach for the detection of Toxoplasma oocysts in water.