Long-term survival of Naegleria polaris from Antarctica after 10 years of storage at 4 °C

A free-living amoeba, Naegleria is ubiquitously distributed in various natural environments. Since some Naegleria spp. are exclusively distributed in the Arctic and sub-Antarctic regions, we hypothesized that the amoeba may be useful to determine long-term survival of Naegleria in laboratory conditions at 4 °C. The main objective of the study is to determine that a species of an environmental amoebal isolated can live at low temperatures after a long time. Here, we therefore show long-term survival of an amoeba, Naegleria polaris isolated from a sediment sample, which was collected from Antarctica 10 years ago, and since stored at 4 °C. The sample was put on non-nutrient agar plates with heat-killed Escherichia coli, and then the plate was incubated at 4, 15, or 30 °C. Motile amoebae were seen only when the plate was incubated at 15 °C. The sequencing of ribosomal DNA including internal transcribed spacers (ITS) 1, 5.8S rDNA, and ITS2 region revealed the amoebae to be N. polaris, which is exclusively distributed in the Arctic and sub-Antarctic regions. Scanning electron microscopic observation showed that no typical sucker-like structure was seen on the surface of N. polaris, but the cysts were similar to those of Naegleria fowleri. Thus, our result shows, for the first time, that N. polaris can survive after 10 years of storage at 4 °C. This finding may help us understand the still undescribed effects of environmental samples on viability of amoebae.

Detection of Naegleria species in environmental samples from Peninsular Malaysia

BACKGROUND

In Malaysia, researchers and medical practitioners are unfamiliar with Naegleria infections. Thus little is known about the existence of pathogenic Naegleria fowleri, and the resultant primary amoebic meningoencephalitis (PAM) is seldom included in the differential diagnosis of central nervous system infections. This study was conducted to detect the presence of Naegleria species in various environmental samples.

METHODS/FINDINGS

A total of 41 Naegleria-like isolates were isolated from water and dust samples. All these isolates were subjected to PCR using two primer sets designed from the ITS1-ITS2 regions. The N. fowleri species-specific primer set failed to produce the expected amplicon. The Naegleria genus-specific primers produced amplicons of 408 bp (35), 450 bp (2), 457 bp (2) or 381 bp (2) from all 41 isolates isolated from aquatic (33) and dust (8) samples. Analysis of the sequences from 10 representative isolates revealed that amplicons with fragments 408, 450 and 457 bp showed homology with non-pathogenic Naegleria species, and 381 bp showed homology with Vahlkampfia species. These results concurred with the morphological observation that all 39 isolates which exhibited flagella were Naegleria, while 2 isolates (AC7, JN034055 and AC8, JN034056) that did not exhibit flagella were Vahlkampfia species.

CONCLUSION

To date, pathogenic species of N. fowleri have not been isolated from Malaysia. All 39 isolates that produced amplicons (408, 450 and 457 bp) from the genus-specific primers were identified as being similar to nonpathogenic Naegleria. Amplicon 408 bp from 5 representative isolates showed 100% and 99.7% identity to Naegleria philippinensis isolate RJTM (AM167890) and is thus believed to be the most common species in our environment. Amplicons 450 bp and 457 bp were respectively believed to be from 2 new species of Naegleria, since representative isolates showed lower homology and had a longer base pair length when compared to the reference species in the Genbank, Naegleria schusteri (AJ566626) and Naegleria laresi (AJ566630), respectively.

Survey of pathogenic free-living amoebae and Legionella spp. in mud spring recreation area

Acanthamoeba, Hartmannella, and Naegleria are free-living amoebae, ubiquitous in aquatic environments. Several species within these genera are recognized as potential human pathogens. These free-living amoebae may facilitate the proliferation of their parasitical bacteria, such as Legionella. In this study, we identified Acanthamoeba, Hartmannella, Naegleria, and Legionella using various analytical procedures and investigated their occurrence at a mud spring recreation area in Taiwan. We investigated factors potentially associated with the prevalence of the pathogens, including various water types, and physical and microbiological water quality parameters. Spring water was collected from 34 sites and Acanthamoeba, Hartmannella, Naegleria, and Legionella were detected in 8.8%, 35.3%, 14.7%, and 47.1%, respectively. The identified species of Acanthamoeba included Acanthamoeba castellanii and Acanthamoeba polyphaga. Nearly all the Hartmannella isolates are identified as Hartmannella vermiformis. The Naegleria species included Naegleria australiensis and its sister groups, and two other isolates referred to a new clade of Naegleria genotypes. The Legionella species identified included unnamed Legionella genotypes, Legionella pneumophila serotype 6, uncultured Legionella spp., Legionella lytica, Legionella drancourtii, and Legionella waltersii. Significant differences (Mann-Whitney U test, P<0.05) were observed between the presence/absence of Hartmannella and total coliforms, between the presence/absence of Naegleria and heterotrophic plate counts, and between the presence/absence of Legionella and heterotrophic plate counts. This survey confirms that pathogenic free-living amoebae and Legionella are prevalent in this Taiwanese mud spring recreation area. The presence of pathogens should be considered a potential health threat when associated with human activities in spring water.

Quantitative Detection and Differentiation of Free-Living Amoeba Species Using SYBR Green–Based Real-Time PCR Melting Curve Analysis

Real-time polymerase chain reaction melting curve analysis (MCA) allows differentiation of several free-living amoebae species. Distinctive characteristics were found for Naegleria fowleri, N. lovaniensis, N. australiensis, N. gruberi, Hartmanella vermiformis, and Willaertia magna. Species specificity of the amplicons was confirmed using agarose gel electrophoresis and sequence-based approaches. Amplification efficiency ranged from 91% to 98%, indicating the quantitative potential of the assay. This MCA approach can be used for quantitative detection of free-living amoebae after cultivation but also as a culture-independent detection method.

Rapid, sensitive, and discriminating identification of Naegleria spp. by real-time PCR and melting-curve analysis

The free-living amoeboflagellate genus Naegleria includes one pathogenic and two potentially pathogenic species (Naegleria fowleri, Naegleria italica, and Naegleria 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 only N. fowleri or require full sequencing to identify other species in the genus. A novel closed-tube method for distinguishing thermophilic Naegleria species 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 seven Naegleria species and the related Willaertia 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.

Molecular identification of free-living amoebae of the Vahlkampfiidae and Acanthamoebidae isolated in Arizona (USA)

Sediment samples from rivers, canals and lakes in Arizona (USA) were cultured for free-living amoebae at three different incubation temperatures (22, 37 and 40 degrees C). Isolates belonging to the Vahlkampfiidae were identified by sequencing the PCR-amplified ITS1, 5.8S and ITS2 rDNA. With this molecular method three Naegleria spp. were identified, N. gruberi sensu stricto, N. australiensis and N. tihangensis. Also a strain each of Willaertia magna and Vahlkampfia avara were identified. Three samples yielded two new Tetramitus spp. of which the closest relative is T. ovis. Many Acanthamoeba strains were also isolated. The genotype of these strains was identified using Acanthamoeba-specific primers (JDP1 and JDP2) amplifying a part of the SSUrDNA and sequencing with an internal primer (892c). Five of the Acanthamoeba isolates belong to genotype T5 (A. lenticulata), while five are genotype T4.

[Infections caused by free-living amebas. Historical commentaries, taxonomy and nomenclature, protozoology and clinicopathologic features]

Infections caused by free-living amebae constitute one of emergent opportunistic infections with greatest medical interest. Although infrequently, they have been described in almost all world, its diagnosis depends on a high index of suspicion, especially in morpho-pathologic and laboratory studies. Exciting historical features of infections due to free-living amebae, its taxonomy and the present nomenclature are briefly reviewed. An analysis of the protozoology of the most frequent agents is done and, based on the author's own experience and the published one, already established anatomo-clinical entities are described: the primary amebic meningoencephalitis, granulomatous amebic encephalitis, Acanthamoeba keratitis, cutaneous acanthamoebiasis, disseminated infection and other rare isolated locations.

Fish-isolated Naegleria strains and their phylogeny inferred from ITS and SSU rDNA sequences

Effort was made to identify Naegleria strains isolated from organs of fish, using phylogenetic analyses of SSU rDNA and ITS sequences. Eighteen fish-isolated strains studied enlarged substantially the so far available set of Naegleria strains characterized by both molecular markers. The phylogenetic analyses of separate and concatenated SSU rDNA and ITS sequences revealed phylogenetic relationships of strains under study; however, they failed to solve classification of fish-isolated strains into species. The sequence similarity of strain-representatives of Naegleria species as well as data obtained on intragenomic variation of ITS sequences discouraged the authors from the definition of new species. The results of the present study provide evidence of a need to re-evaluate the current practice of setting boundaries between species of the genus Naegleria. Sequences obtained in this study have been deposited in GenBank with accession numbers DQ768714-DQ768743.

Isolation and molecular identification of free-living amoebae of the genus Naegleria from Arctic and sub-Antarctic regions

Twenty-three freshwater samples with sediment taken from two regions in the Arctic, Spitzbergen and Greenland, and one region in sub-Antarctica, Ile de la Possession, were cultured for amoebae at 37 degrees C and room temperature (RT). Only two samples yielded amoebae at 37 degrees C and the two isolates were identified from their morphological features to belong to the genus Acanthamoeba. Vahlkampfiid amoebae were isolated from 11 samples at RT. Morphological analysis of the cysts identified all 11 isolates as belonging to the genus Naegleria, although only about half of them (45%) transformed into flagellates. Ribosomal DNA sequence analysis demonstrated that these isolates represent novel species and that N. antarctica, N. dobsoni and N. chilensis are their closest relatives. Not surprisingly, these three species also grow at lower temperatures (<37 degrees C) than the majority of described Naegleria spp. Two of the eight new species were found in both Arctic and sub-Antarctic regions, and other new species from the Arctic are closely related to new species from the sub-Antarctic. Therefore, it seems the Naegleria gene pool present in the polar regions is different from that found in temperate and tropical regions.

Evolution of four gene families with patchy phylogenetic distributions: influx of genes into protist genomes

BACKGROUND

Lateral gene transfer (LGT) in eukaryotes from non-organellar sources is a controversial subject in need of further study. Here we present gene distribution and phylogenetic analyses of the genes encoding the hybrid-cluster protein, A-type flavoprotein, glucosamine-6-phosphate isomerase, and alcohol dehydrogenase E. These four genes have a limited distribution among sequenced prokaryotic and eukaryotic genomes and were previously implicated in gene transfer events affecting eukaryotes. If our previous contention that these genes were introduced by LGT independently into the diplomonad and Entamoeba lineages were true, we expect that the number of putative transfers and the phylogenetic signal supporting LGT should be stable or increase, rather than decrease, when novel eukaryotic and prokaryotic homologs are added to the analyses.

RESULTS

The addition of homologs from phagotrophic protists, including several Entamoeba species, the pelobiont Mastigamoeba balamuthi, and the parabasalid Trichomonas vaginalis, and a large quantity of sequences from genome projects resulted in an apparent increase in the number of putative transfer events affecting all three domains of life. Some of the eukaryotic transfers affect a wide range of protists, such as three divergent lineages of Amoebozoa, represented by Entamoeba, Mastigamoeba, and Dictyostelium, while other transfers only affect a limited diversity, for example only the Entamoeba lineage. These observations are consistent with a model where these genes have been introduced into protist genomes independently from various sources over a long evolutionary time.

CONCLUSION

Phylogenetic analyses of the updated datasets using more sophisticated phylogenetic methods, in combination with the gene distribution analyses, strengthened, rather than weakened, the support for LGT as an important mechanism affecting the evolution of these gene families. Thus, gene transfer seems to be an on-going evolutionary mechanism by which genes are spread between unrelated lineages of all three domains of life, further indicating the importance of LGT from non-organellar sources into eukaryotic genomes.

Morphologic and Molecular Identification ofNaegleria dunnebackein. sp. Isolated from a Water Sample

Naegleria dunnebackei n. sp., a new species of the free-living amoeboflagellate Naegleria, is described in this report. The organism was isolated from a water sample taken from drinking troughs associated with cases of primary amoebic meningoencephalitis in cattle at a ranch in southern California. The isolate grew at, but not above 37 degrees C, and did not kill young mice upon intranasal inoculation suggesting that it was not pathogenic. The new species combines morphological features of non-pathogenic Naegleria gruberi and pathogenic Naegleria fowleri. The trophic amoeba resembled other members of the genus, with a prominent vesicular nucleus and mitochondria with discoidal cristae; a Golgi apparatus was not observed by electron microscopy. The cyst stage had pores in the wall typical of those seen in pathogenic N. fowleri. Upon suspension in distilled water, amoebae transformed into temporary, non-feeding flagellates, mostly with two anterior flagella but occasionally with four. The rationale for its description as a new species was based upon sequencing of the 5.8S rDNA and internal transcribed spacers of the amoeba, which is similar to but not identical to that of Naegleria gallica, differing from that organism's DNA by six base pairs. Virus-like elements were found in the cytoplasm of trophic amoebae, often in association with crystalloids, and may be the cause of lysis of amoebae in culture.

The isolation of Naegleria italica from Peru indicates that this potentially pathogenic species occurs worldwide

The amoeboflagellate genus Naegleria includes a few species that are virulent in experimental animals. One of these species, Naegleria italica, has been isolated from the environment only in Italy and Australia. I report here the isolation of a strain of N. italica from a water sample collected in Peru. This broadens the occurrence of this species to encompass three different continents. This new N. italica isolate from Peru has the same ITS1, 5.8S rDNA and ITS2 sequence as that of the type strain from Italy and the isolate from Australia. From the same water body in Peru a Naegleria strain was isolated that differs from N. italica by only one additional base pair in the ITS2 sequence. The maximum growth temperature tolerated by this particular isolate is 40 degrees C, which is different from that of N. italica, which is 42 degrees C.

Pathogenic free-living amoebae in Korea

Acanthamoeba and Naegleria are widely distributed in fresh water, soil and dust throughout the world, and cause meningoencephalitis or keratoconjunctivitis in humans and other mammals. Korean isolates, namely, Naegleria sp. YM-1 and Acanthamoeba sp. YM-2, YM-3, YM-4, YM-5, YM-6 and YM-7, were collected from sewage, water puddles, a storage reservoir, the gills of a fresh water fish, and by corneal washing. These isolates were categorized into three groups based on the mortalities of infected mice namely, highly virulent (YM-4), moderately virulent (YM-2, YM-5 and YM-7) and nonpathogenic (YM-3). In addition, a new species of Acanthamoeba was isolated from a freshwater fish in Korea and tentatively named Korean isolate YM-4. The morphologic characters of its cysts were similar to those of A. culbertsoni and A. royreba, which were previously designated as Acanthamoeba group III. Based on experimentally infected mouse mortality, Acanthamoeba YM-4 was highly virulent. The isoenzymes profile of Acanthamoeba YM-4 was similar to that of A. royreba. Moreover, an anti-Acanthamoeba YM-4 monoclonal antibody reacted only with Acanthamoeba YM-4, and not with A. culbertsoni. Random amplified polymorphic DNA marker analysis and RFLP analysis of mitochondrial DNA and of a 18S small subunit ribosomal RNA, placed Acanthamoeba YM-4 in a separate cluster based on phylogenic distances. Thus Acanthamoeba YM-4 was identified as a new species, and assigned Acanthamoeba sohi. Up to the year 2002 in Korea, two clinical cases were found to be infected with Acanthamoeba spp. These patients died of meningoencephalitis. In addition, one case of Acanthamoeba pneumonia with an immunodeficient status was reported and Acanthamoeba was detected in several cases of chronic relapsing corneal ulcer, chronic conjunctivitis, and keratitis.

Detection of Naegleria sp. in a thermal, acidic stream in Yellowstone National Park

An initial survey of sequences of PCR-amplified portions of the 18S rRNA genes from a community DNA clone library, prepared from an algal mat in a thermal, acidic stream in Yellowstone National Park, WY, USA, revealed among other sequences, several that matched Vahlkampfia. This finding prompted further investigation using primers specific for Naegleria. Sequences from a subsequent DNA clone library, prepared from the 5.8S rRNA gene and the adjacent internal transcribed spacer (ITS) regions of the rRNA, closely matched Naegleria and formed an independent lineage within a clade containing Naegleria sturti and Naegleria niuginiensis. The sequences may represent a new Naegleria species.

Genetic variations in the internal transcribed spacer and mitochondrial small subunit rRNA gene of Naegleria spp

Naegleria spp. are widely distributed free-living amebas, but one species in the genus, N. fowleri, causes acute fulminant primary amebic meningoencephalitis in humans and other animals. Thus, it is important to differentiate N. fowleri from the rest in the genus of Naegleria, and to develop tools for the detection of intra-specific genetic variations. In this study, one isolate each of N. australiensis, N. gruberi, N. jadini, and N. lovaniensis and 22 isolates of N. fowleri were characterized at the internal transcribed spacers (ITS) and mitochondrial small subunit rRNA (mtSSU rRNA) gene. The mtSSU rRNA primers designed amplified DNA of all isolates, with distinct sequences obtained from all species examined. In contrast, the ITS primers only amplified DNA from N. lovaniensis and N. fowleri, with minor sequence differences between the two. Three genotypes of N. fowleri were found among the isolates analyzed in both the mtSSU rRNA gene and ITS. The extent of sequence variation was greater in the mtSSU rRNA gene, but the ITS had the advantage of length polymorphism. These data should be useful in the development of molecular tools for rapid species differentiation and genotyping of Naegleria spp.

Detection and significance of the potentially pathogenic amoeboflagellate Naegleria italica in Australia

Thermophilic amoeboflagellates in the genus Naegleria include both virulent and benign species. One of the less studied species, N. italica, has not been detected in the environment since the first reports from Italy in the 1980s; its virulence is known only from infection of laboratory mice. Two recent strains from recreational water in Western Australia (AWQC NG960, NG961) were tentatively identified as N. italica from the characteristic mobilities of seven isozymes. Sequences of the 5.8S rRNA gene and its flanking ITS aligned with a 380+bp length of the published sequence for N. italica with 98% identity. Differences from the type strain were confined to ITS2. Shorter alignments (<320 bp) were observed with other Naegleria species, corresponding to conserved regions of the 5.8S gene and ITS. Unlike the European type strain of N. italica, the Australian isolates failed to infect laboratory mice intranasally, confirming that infectivity of this species is variable and often lower than in N. fowleri.

Molecular Definition and the Ubiquity of Species in the Genus

To investigate the variability within species of the genus Naegleria, the ITS1,5.8S and ITS2 rDNA were sequenced of several strains of N. lovaniensis and its Western Australian variants, N. australiensis, N. fowleri, N. andersoni, N. jamiesoni, N. tihangensis, N. pringsheimi, N. pagei, N. gruberi sensu lato and a Naegleria lineage that lost a group I intron from the SSUrDNA twintron. As a result, it is possible to define a molecular species within the Naegleria genus. In addition, one strain of each different allozyme cluster was sequenced to investigate whether they belong to described species or should be treated as distinct new species. This leads to the proposal of eleven new species. The sequencing results from those Naegleria spp. of which several strains are available indicate that these species are ubiquitous. The only exception might be the species represented by the WA variants. However, there are still many Naegleria spp. for which only one strain has been isolated, hence, it is important that the search for more isolates should be continued worldwide.

A brief survey of free-living amebae in Thailand and Hamamatsu District, Japan

The aim of this study was to determine the presence of free-living amebae in aquatic habitats of human environments in Thailand and Hamamatsu district, Japan. Genus identification was based on the morphology of cyst and trophozoite forms and a flagellation test for genus Naegleria. The pathogenic potential was tested in mice by nasal instillation for genus Naegleria and Acanthameba. In 14 provinces of Thailand, amebae were isolated in 43 from 95 water samples and 67 from 120 soil swabs. Amebae of 49 isolates from waters were identified as Acanthameba (36.7%), Naegleria (28.6%), Hartmannella (20.4%), Vahlkampfia (12.2%) and Vannella (2%). Soil samples have significantly higher levels of Acanthameba and Hartmannella (p<0.05) but lower for Naegleria (p<0.05) and 7 unidentified amebae were found. In Hamamatsu district, Japan, 62 amebae of the same genera were isolated from 47 of 95 water samples. There were significantly higher levels of Acanthameba (22.6%) (p<0.05) but lower for Naegleria (4.8%) (p<0.05) than those of Thailand which each of them caused death in mice. Three unidentified amebae were isolated. This finding serves as additional evidence for the presence of free-living amebae under natural and the difference in distribution between tropic and subtropic areas.

Use of multiplex PCR and PCR restriction enzyme analysis for detection and exploration of the variability in the free-living amoeba Naegleria in the environment

A multiplex PCR was developed to simultaneously detect Naegleria fowleri and other Naegleria species in the environment. Multiplex PCR was also capable of identifying N. fowleri isolates with internal transcribed spacers of different sizes. In addition, restriction fragment length polymorphism analysis of the PCR product distinguished the main thermophilic Naegleria species from the sampling sites.

Identity of Naegleria strains isolated from organs of freshwater fishes

Eighteen Naegleria strains were isolated from organs of freshwater fishes belonging to 5 species. Morphometric study allowed the separation of the Naegleria strains from the non-vahlkampfiid amoeboflagellates, but was inadequate for species determination. Six strains, representatives of groups that had a slightly different cyst size, were selected and corresponding derived clones were subjected to sequence analysis and riboprinting restriction fragment length polymorphism (RFLP)-PCR analysis of the small subunit (SSU) rRNA genes. One strain isolated from the brain of a fish with systemic infection was characterised by an intronless 2 kb long SSU rRNA gene and was identified as N. australiensis. Another 5 strains had a 1.3 kb long group I intron in their SSU rRNA gene and, based on the SSU rRNA sequences and riboprints, RFLP-PCR patterns appeared in phylogenetic trees to be closely related to Naegleria clarki.

The amoeba-to-flagellate transformation test is not reliable for the diagnosis of the genus Naegleria. Description of three new Naegleria spp

Trophozoites of several isolates from one location in Australia have failed consistently to transform into flagellates, although they display all other characteristics of the genus Naegleria. When changing the standard transformation test, flagellates were produced. In phylogenetic trees derived from partial small subunit ribosomal DNA (SSUrDNA) sequences, one of these strains branches close to a cluster comprising N. clarki, N. australiensis, N. italica and N. jadini. It is proposed that these Australian isolates represent a new species, named N. fultoni (strain NG885). Failing to form flagellates since their isolation, even when different transformation procedures are used, are two Naegleria strains from Chile and Indonesia. In SSUrDNA-based phylogenetic trees the Chilean strain clusters with N. pussardi and the Indonesian strain clusters with N. galeacystis, but the degree of sequence difference from these described species (3.5% and 2.2%, respectively) is sufficient to propose that both of the strains represent new species, named N. chilensis (strain NG946) and N. indonesiensis (strain NG945), respectively. The close relationships between each of the new species and the Naegleria species with which they cluster in SSUrDNA-based trees were confirmed by ribosomal internal transcribed spacer region (ITS) sequence comparisons. In France, several non-flagellating N. fowleri strains were isolated from one location. ITS rDNA sequence comparisons indicated that they correspond to a 'type' of N. fowleri found in both Europe and the USA. A redefinition of the genus Naegleria is proposed as a consequence of these and previous findings.

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.

Isolation and identification by partial sequencing of the 18S ribosomal gene of free-living amoebae from necrotic tissue of Basilliscus plumifrons (Sauria: Iguanidae)

A 3-year-old Basiliscus plumifrons developed a necrotic lesion on the tail resulting from nodules of unknown etiology. Investigation of necrotic tissue revealed several gram-negative bacteria as well as three different species of free-living amoebae. The amoebae were identified by morphological characters as belonging to the genera Acanthamoeba, Echinamoeba, and Naegleria, respectively. Partial sequencing of the 18S ribosomal gene was performed for reliable systematic determination. Two of the isolates showed thermotolerance. No isolate was growable in conventional liquid media, but the Acanthamoeba strain readily grew on a human cell line (HEp2). It remains unclear whether the amoebae fed on the coexisting bacteria or on host tissue.

Evidence for the Heterolobosea from phylogenetic analysis of genes encoding glyceraldehyde-3-phosphate dehydrogenase

The phylogenetic relationships between major slime mould groups and the identification of their unicellular relatives has been a subject of controversy for many years. Traditionally, it has been assumed that two slime mould groups, the acrasids and the dictyostelids were related by virtue of their cellular slime mould habit; a view still endorsed by at least one current classification scheme. However, a decade ago, on the basis of detailed ultrastructural resemblances it was proposed that acrasids of the family Acrasidae were not relatives of other slime moulds but instead related to a group of mostly free-living unicellular amoebae, the Schizopyrenida. The class Heterolobosea was created to contain these organisms and has since figured in many discussions of protist evolution. We sought to test the validity of Heterolobosea by characterizing homologs of the highly conserved glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) from an acrasid, Acrasis rosea; a dictyostelid, Dictyostelium discoideum; and the schizopyrenid Naegleria andersoni. Phylogenetic analysis of these and other GAPDH sequences, using maximum parsimony, neighbour-joining distance and maximum likelihood methods strongly supports the Heterolobosea hypothesis and discredits the concept of a cellular slime mould grouping. Moreover, all of our analyses place Dictyostelium discoideum as a relatively recently originating lineage, most closely related to the Metazoa, similar to other recently published phylogenies of protein-coding genes. However, GAPDH phylogenies do not show robust branching orders for most of the relationships between major groups. We propose that several of the incongruencies observed between GAPDH and other molecular phylogenies are artifacts resulting from substitutional saturation of this enzyme.

Use of monoclonal antibodies to distinguish pathogenic Naegleria fowleri (cysts, trophozoites, or flagellate forms) from other Naegleria species

Monoclonal antibodies (MAbs) reactive to the pathogenic amoeba Naegleria fowleri were analyzed by enzyme-linked immunosorbent assay (ELISA), indirect immunofluorescence assay, Western blotting (immunoblotting), and radioimmunoprecipitation assay (RIPA). Two MAbs (3A4 and 5D12) showed reactivity by ELISA with all N. fowleri strains tested and no reactivity with the five other Naegleria species, N. lovaniensis, N. gruberi, N. australiensis, N. jadini, and N. andersoni. These MAbs reacted with the three morphological forms of N. fowleri (trophozoites, cysts, and flagellates). The reactivity on Western blots was suppressed by treatment with metaperiodate, suggesting a carbohydrate epitope. Differences in reactivity patterns between trophozoites and cysts observed with radioimmunoprecipitation assay might reflect differences in biological properties. The formalin stability of the epitope may be useful in detecting N. fowleri in fixed biopsies and in investigating the pathological process.

Differentiation of Naegleria fowleri and other Naegleriae by polymerase chain reaction and hybridization methods

In order to detect and identify Naegleria fowleri strains an assay based on the Polymerase Chain Reaction (PCR) was evaluated. The amplified DNA fragments were detected by gel electrophoresis and ethidium bromide staining, followed by Southern blot hybridization with an internal digoxigenin-labeled probe. A set of primers (B1B2) which flank a 678-bp region within a virulence-associated gene, allowed for the highly specific identification of N. fowleri, since Naegleriae (N. lovaniensis, N. australiensis, N. gruberi, N. andersoni and N. jadini) and other Protozoa did not react. These primers did not detect amplification products from various organisms: Gram-positive bacteria, Gram-negative bacteria, algae, yeasts and human DNA. Whereas a second set of primers (A1A2), which flank a different sequence, detected various Naegleriae and Acanthamoebae strains. After 40 amplification cycles, the limit of detection was a single cell (cyst or trophozoite). Thus, the PCR appears to be a rapid and powerful tool for identification and detection of N. fowleri.

Discontinuous genetic variation among mesophilic Naegleria isolates: further evidence that N. gruberi is not a single species

Naegleria isolates which are currently placed in the type species N. gruberi display great genetic, physiological and morphological heterogeneity. There are two possible interpretations of the nature of this species--that N. gruberi is a species complex or that it is a single continuously variable species. To distinguish between these alternatives, allelic states were determined for 33 loci in 74 new isolates selected to represent wide geographic sources and diverse temperature limits for growth. The results were compared with data for culture collection strains of N. gruberi and other species in the genus. The isolates formed a discontinuous series of clusters, separated by genetic distances similar to those separating the better-characterised taxa N. fowleri, N. lovaniensis, N. jadini, N. australiensis australiensis and N. australiensis italica. Culture collection strains assigned to N. gruberi fell into six distinct clusters, while other clusters were not represented by reference strains. The data are most consistent with the interpretation that N. gruberi is a group of several distinct species, each equivalent to the recently described species in the genus. Naegleria andersoni andersoni and N. andersoni jamiesoni also formed two distinct clusters, equivalent to species. Characteristics temperature limits for growth show that the mesophilic species are ecological as well as genetic entities.

Free-living amoebae in Egypt. 1. Naegleria gruberi and Naegleria fowleri

Two Naegleria species were isolated and identified from various water sources in Lower and Upper Egypt. Identification was based on the morphology, nuclear division and the excystation and flagellation tests. The trophic, cystic and flagellate forms of N. gruberi are larger than those of N. fowleri and the cyst of the former species has one or more pores while that of the latter species has no pores and has an outer gelatinous layer. The size and the morphological characteristics of these two free-living amoebae from Egypt were in complete agreement with those previously described for amoebae of this same genus and species endemic to other geographical areas.

Naegleria lovaniensis tarasca new subspecies, and the purepecha strain, a morphological variant of N. l. lovaniensis, isolated from natural thermal waters in Mexico

Amoebae were isolated from a natural thermal water source in Michoacán, Mexico, in September 1986. Two 500-ml samples were taken from pools with water at 45 degrees C and 46 degrees C and concentrated at 2,000 g for 15 min. The sediment was seeded on nonnutritive agar plates and incubated at 42 degrees C. The isolates were axenized in bactocasitone-serum medium. The identification of the isolates was based on their morphology, total protein and isoenzyme patterns by agarose isoelectric focusing, serology, fine structure, agglutination with Concanavalin A, sensitivity to trimethoprim, capacity to kill mice, and their cytopathic effect in Vero cells. The results showed several morphophysiological, biochemical and serological differences between the isolates and the type strain Aq/9/1/45D of Naegleria lovaniensis. These remarkable differences provide sufficient evidence to consider one of the isolates a new subspecies, and the other one a morphological variant of N. l. lovaniensis, which can be differentiated from other Naegleriae by their morphology, biochemistry, serology and physiology. The authors propose the name tarasca for the subspecies and purepecha for the morphological variant.

A genetic approach to species criteria in the amoeba genus Naegleria using allozyme electrophoresis

The present study employs allozyme electrophoresis to characterize and inter-relate 61 isolates of Naegleria. Diploidy was confirmed, with heterozygotes observed at 29 of the 33 loci established and in all but two isolates. With a single exception, isolates clustered at two levels of similarity, either below 21% or above 52%. It is argued that such a major discontinuity provides a sound biological basis for a species concept in Naegleria. On this basis the present species-level taxonomy does not reflect the genetic diversity of the genus. The study recognized 18 genetic groups of species rank. The subspecies N. australiensis italica deserves specific rank; additional thermophilic species not closely related to N. fowleri and N. lovaniensis are recognized; and N. gruberi as currently conceived is a complex of 10 species, at least five of which are represented in the formal culture collections. Most species are genetically too different for relationships to be elucidated by allozyme electrophoresis, supporting the view that some of the times of divergence within the genus are extremely ancient.

A temporary flagellate (mastigote) stage in the vahlkampfiid amoeba Willaertia magna and its possible evolutionary significance

A temporary flagellate (mastigote) stage has been observed in several isolates of the vahlkampfiid amoeba Willaertia magna. In an Australian isolate studied in detail, flagellates appeared synchronously, although later than in Naegleria fowleri or N. lovaniensis under similar conditions (half-maximal time, t50 = 168 min at 37 degrees C). The flagellates initially have four flagella and lack a cytostome, but undergo several successive divisions, the first of them synchronous, resulting in progressive reduction in cell volume. New flagella appear during and after division, and the number of flagella in daughter cells of later divisions is rather variable. Comparison of these observations with descriptions of other amoeboflagellates confirms that Willaertia is a valid genus. A likely sequence of morphological changes in the evolution of Willaertia and Naegleria from a hypothetical ancestral vahlkampfiid is proposed.

Application of isoenzymatic typing to the identification of nonaxenic strains of Naegleria (Protozoa, Rhizopoda)

Isoenzymatic typing of the different species of Naegleria was studied by comparing isoelectric focusing on axenic and nonaxenic strains using the most discriminating enzymes: lactate dehydrogenase (LDH), malic enzyme (ME), beta-hydroxybutyrate dehydrogenase (beta-HBDH), superoxide dismutase (SOD), and acid phosphatase (AP). The results show that bacteria in nonaxenic cultures have no influence on the interpretation of zymograms. The specificity of the enzymatic patterns of each strain is maintained in all of these enzymatic systems except LDH. With SOD, the existence of a supplementary isoenzyme among all of the nonaxenic strains is probably linked to an enzymatic induction phenomenon.

Restriction endonuclease analysis of mitochondrial DNA as an aid in the taxonomy of Naegleria and Vahlkampfia

Using restriction enzyme analysis, mitochondrial DNA fragment patterns from seven strains of pathogenic and nonpathogenic Naegleria and one strain of Vahlkampfia were compared to estimate nucleotide sequence divergence. Significantly high levels of estimated genetic variation between strains of N. gruberi, N. fowleri, and N. jadini support the current taxonomic level of the individual Naegleria species and suggest a distinct phylogeny for each group. Naegleria lovaniensis, strain TS, was shown to have significant nucleotide sequence homology with N. gruberi, strain EGs, suggesting that the two groups share a close taxonomic relationship. The pathogenic strain MB-41 of N. fowleri exhibited distinct genetic divergence from the highly homologous, pathogenic strain Nf66 and the drug-cured strain 6088. Morphologically distinct strains EGs and 1518/la of N. gruberi exhibited significantly large sequence divergence consistent with a more distant taxonomic relationship. Amoebae from the genus Vahlkampfia expressed genetic similarity with strains of N. gruberi.

[First isolation in Italy of Naegleria australiensis (De Jonckheere, 1981)]

An epidemiological investigation was carried out in Northern Italian spa to detect presence and incidence of free-living amoebae, mostly belonging to amphizoic species Acanthamoeba and Naegleria. Seven pathogenic strains of Naegleria spp. were isolated. Morpho-biological characterization and indirect immunofluorescence assays showed that all these strains belong to N. australiensis, a new pathogenic species. Such a species could induce, along with N. fowleri and Acanthamoeba spp., fatal meningo-encephalitis in man and other mammals.