A duplex real-time PCR assay for the quantitative detection of Naegleria fowleri in water samples.

A fast and accurate duplex real-time PCR (qPCR) was developed to detect and quantify the human pathogenic amoeba Naegleria fowleri in water samples. In this study, primers and probe based on the Mp2Cl5 gene were designed to amplify and quantify N. fowleri DNA in a single duplex reaction. The qPCR detection limit (DL) corresponds to the minimum DNA quantity showing significant fluorescence with at least 90% of the positive controls in a duplex reaction. Using fluorescent Taqman technology the qPCR was found to be 100% specific for N. fowleri with a DL of 3 N. fowleri cell equivalents and a PCR efficiency of 99%. The quantification limit (QL) was 16 N. fowleri cell equivalents (corresponded with 320 N. fowleri cell equivalents l(-1) water sample) in a duplex qPCR reaction and corresponds to the lowest DNA quantity amplifiable with a coefficient of variation less than 25%. To detect inhibition an exogenous internal positive control (IPC) was included in each PCR reaction preventing false negative results. Comparison of qPCR and most probable number (MPN) culture results confirms that the developed qPCR is well suited for rapid and quantitative detection of this human pathogen in real water samples. Nevertheless 'low contamination levels' of water samples (<200 N. fowleri cells l(-1)) still require culture method analyses. When other thermophilic Naegleria are very dominant, the MPN culture method could result in an underestimation in the real number of N. fowleri and some caution is necessary to interpret the data. The N. fowleri qPCR could be a useful tool to study further competitive phenomena between thermophilic Naegleria strains.