Bret S. Robinson

The free-living amoeboflagellate genusNaegleriaincludes one pathogenic and two potentially pathogenic species (Naegleria fowleri,Naegleria italica, andNaegleria australiensis) plus numerous benign organisms. Monitoring of bathing water, water supplies, and cooling systems for these pathogens requires a timely and reliable method for identification, but current DNA sequence-based methods identify onlyN. fowlerior require full sequencing to identify other species in the genus. A novel closed-tube method for distinguishing thermophilicNaegleriaspecies is presented, using a single primer set and the DNA intercalating dye SYTO9 for real-time PCR and melting-curve analysis of the 5.8S ribosomal DNA gene and flanking noncoding spacers (ITS1, ITS2). Collection of DNA melting data at close temperature intervals produces highly informative melting curves with one or more recognizable melting peaks, readily distinguished for sevenNaegleriaspecies and the relatedWillaertia magna. Advantages over other methods used to identify these organisms include its comprehensiveness (encompassing all species tested to date), simplicity (no electrophoresis required to verify the product), and sensitivity (unambiguous identification from DNA equivalent to one cell). This approach should be applicable to a wide range of microorganisms of medical importance.