Comparison between two real-time PCR assays and a nested-PCR for the detection of Toxoplasma gondii

In recent years, the diagnosis of toxoplasmosis has been improved by Real-time PCR assays. In this study we compared the performances of two Real-time PCRs (FRET and TaqMan protocols) already described in the literature, and one nested-PCR, currently used in our laboratory for the molecular diagnosis of toxoplasmosis.

We evaluated the sensitivity and the specificity of a FRET- and a TaqMan-based Real-time PCRs targeting a 529 bp repeat region and the 18S RNA gene, respectively, and a nested-PCR, targeting the B1-gene of Toxoplasma gondii. We also tested, through nested-PCR, 46 biological samples obtained during a period of 29 months from pregnant women or immunocompromised patients with suspected T. gondii infection.

The analytical sensitivity of nested and TaqMan PCRs was approximately 10(3) tachyzoites/ml. FRET assay showed a sensitivity of 102 tachyzoites/ml. Three out of 46 biological samples were nested-PCR-positive and these results were also confirmed by both Real-time PCRs.

Nested- and real-time PCRs evaluated in this study resulted very sensitive and specific; in particular FRET PCR resulted more sensitive than the other assays, probably because of the greater copy number of the target sequence. Real-time PCR assays are easy-to-use, producing results faster than conventional PCR systems and reducing contamination risks.