Naegleria Australiensis Research Articles

Viability of pathogenic Naegleria and Acanthamoeba isolates during 10 years of cryopreservation

This is a follow-up report on the viability of pathogenic Naegleria fowleri, Naegleria australiensis and Acanthamoeba castellanii isolates during 5 to 10 years of cryopreservation at -70 degrees C. The greatest decrease in viability occurred with N. fowleri and the least occurred with N. australiensis. At 10 years of cryostorage, viability was 21% for N. fowleri, 32% for A. castellanii and 51% for N. australiensis.

Analysis of the 5.8S rRNA gene and the internal transcribed spacers in Naegleria spp. and in N. fowleri.

Internal transcribed spacers (ITS) and the 5.8S ribosomal gene of 21 Naegleria fowleri strains and eight other species including Naegleria gruberi were sequenced. The results showed that this region can help differentiate between and within species. The phylogeny of Naegleria spp. deduced from the ITS and the 5.8S gene produced four major lineages, fowleri-lovaniensis, galeacystis-italica-clarki-gruberi-australiensis, andersoni-jamiesoni, and pussardi, that fit perfectly with those inferred from the 18S rRNA gene analysis. The N. gruberi isolate, NG260, was closely related to Naegleria pussardi. The other N. gruberi isolates branched together with Naegleria australiensis in another lineage. The ITS and 5.8S results for N. fowleri were congruent with those previously deduced by RAPD analysis. The phylogenetic analysis inferred from ITS and RAPD data revealed two major groups. The French Cattenom and Chooz and South Pacific strains constituted the first group. The second group encompassed the strains corresponding to the Euro-American and Widespread RAPD variants and shared the same substitution in the 5.8S gene. In addition, it was possible to define species specific primers in ITS regions to rapidly identify N. fowleri.

Evaluation of evolutionary divergence in the genus Naegleria by analysis of ribosomal DNA plasmid restriction patterns

Ribosomal DNA (rDNA) plasmid restriction maps of 10 strains and rDNA hybridisation patterns of 61 additional strains have been used to assess inter- and intra-specific diversity and phylogenetic relationships in the genus Naegleria. The results obtained by this method largely confirm those of previous studies based on a variety of other criteria. They indicate that very little variation exists within the pathogenic species Naegleria fowleri despite its worldwide distribution and that it is closely related to the non-pathogenic Naegleria lovaniensis. Naegleria gruberi is most likely a polyphyletic grouping and care should be taken when using one strain as a reference point for this species. In addition, the two subspecies of the pathogenic Naegleria australiensis arose separately from within the range of variability encompassed by N. gruberi, as did the species Adelphamoeba galeacystis which should probably be assigned to the genus Naegleria. The species Naegleria jadini and Naegleria andersoni are not closely related to any other in the genus based on their rDNA patterns.

Scanning Electron Microscopy of Trophozoites of Naegleria Species

The genus, Naegleria, includes four species of amebae which are either free-living or opportunistic pathogens. Naegleria fowleri, is the causative agent of Primary Amebic Meningoencephalitis, a rare but almost always fatal disease in man. Naegleria australiensis is an environmental isolate which is moderately pathogenic in mice. Naegleria lovaniensis and Naegleria gruberi are nonpathogenic environmental isolates. The four species were examined by scanning electron microscopy in order to determine whether membrane surface extensions, called food cups, could be correlated to pathogenicity. Food cups have been previously identified on the surface of Entamoeba histolytica and N. fowleri. It has been suggested that the food cups or stomas, are associated with internationalization of liquid and particulate components.

Naegleria australiensis: experimental meningoencephalitis in mice

Naegleria australiensis was recently described as a new species of free-living amoeba pathogenic for mice. Infections of human brain by the free-living amoebae N. fowleri and Acanthamoeba spp. are well known. We here describe the clinicopathological features of experimental infection of the central nervous system of mice by N. australiensis. Weanling mice were inoculated intranasally and intracerebrally. The involvement of the nasal mucosa, olfactory neuroepithelium and lobes, cerebrum and cerebellum was detected in haematoxylin-eosin stained paraffin-embedded sections. Amoebic trophozoites sparsely located throughout the central nervous system were shown better by the immunoperoxidase method. Cysts were not detected. The histopathological changes differ from those produced by N. fowleri, especially in the degree of severity. They may be confused with those caused by Acanthamoeba spp. which usually produced subacute and chronic encephalitis with a prolonged clinical course.