Quantitative Real-time Polymerase Chain Reaction for the Accurate Detection of Toxoplasma Gondii in Amniotic Fluid

Infection with Toxoplasma gondii during pregnancy is often asymptomatic and may cause severe fetal damage. A quantitative TaqMan minor groove binder real-time polymerase chain reaction (PCR) assay was developed for the specific and sensitive detection of the previously described 529-bp repeat element occurring up to 200 to 300 times in T. gondii genome. The qualitative and quantitative detection limits determined were 6 and 20 marker copies (1/30 to 1/50 of 1 parasite) per PCR, respectively. In addition to standard PCR cycling conditions, 3 different fast PCR protocols were evaluated to minimize run time. A higher variability but no loss of specificity was observed. For the evaluation of clinical applicability, a total of 135 amniotic fluid samples were analyzed targeting both 529-bp and B1 gene. The sensitivity and specificity were 88.0% and 100.0% for B1, and 100.0% and 98.2% for 529-bp PCR assay (positive predictive value and negative predictive value: 100.0% and 97.4%, and 92.6% and 100.0%, respectively). Our results demonstrated an increased sensitivity of the 529-bp PCR assay even in a faster protocol.