PCR detection and analysis of the free-living amoeba Naegleria in hot springs in Yellowstone and Grand Teton National Parks

Free-living thermotolerant amoebae pose a significant health risk to people who soak and swim in habitats suitable for their growth, such as hot springs. In this survey of 23 different hot springs in Yellowstone and Grand Teton National Parks, we used PCR with primer sets specific for Naegleria to detect three sequence types that represent species not previously described, as well as a fourth sequence type identified as the pathogen Naegleria fowleri.

Effect of antifungal drugs on pathogenic Naegleria spp isolated from natural water sources

Five of 16 strains of pathogenic Naegleria spp isolated from 350 natural water sources in Taling Chan District, Bangkok had similar molecular weights and zymogram patterns to those of Naegleria fowleri CDCVO 3081 and Thai strain. The in vitro effects of antifungal drugs (amphotericin B, ketoconazole, fluconazole and itraconazole) were tested at the following concentrations: amphotericin B 0.01-0.55 microg/ml, ketoconazole 0.01-0.3 microg/ml, fluconazole 0.75-3.5 mg/ml and itraconazole 4-12 mg/ml respectively. Aliquots (15,000 cells/ml) of the amoebae were placed in the cells of the microtiter plate and incubated at 37 degrees C. Amoebae from each treatment sample were exposed to one of the four antifungal drugs. Statistical analysis was done by dependent t-test. The sensitivity of the antifungal drugs (MIC50) was as follows: amphotericin B 0.03-0.035 microg/ml ketoconazole 0.05-0.15 microg/ml fluconazole 1.75 mg/ml and itraconazole 8-9 mg/ml respectively (p < 0.005).

CONCLUSION

Amphotericin B and ketoconazole are more active against Naegleria fowleri in vitro. The results of the present study should be used as an in vitro screening test for drugs that have potential amebicidal activity.

[Isolation of potencially pathogenic free-living amoebas in hospital dust]

OBJECTIVE

To evaluate the occurrence of free-living amoebas of the genera Acanthamoeba and Naegleria is dust samples colleted in two hospitals.

METHODS

One-hundred and thirty-two dust samples were collected in two hospitals in Brazil. Hospital collection sites were the following: intensive care unit, operation rooms, nursery, kitchen, emergency and infectious diseases isolation room. The isolation of the amoebas was performed in three culture media: non-nutrient agar inoculated with Escherichia coli, soy agar, and microculture in Giazzi-modified Pavlova's medium. The amoebas were identified according to morphological criteria.

RESULTS

Amoebas of the genera Acanthamoeba and Naegleria were found in 45.5% of the samples, of which 41.6% were collected in the university hospital and 50% in the state hospital. Of all, 45.5% were positive for the genera Acanthamoeba and 3.8% for genera Naegleria.

CONCLUSIONS

Potentially pathogenic free-living amoebas were seen in all sites of the two hospitals and Acanthamoeba was the most frequently isolated genera.

December 2002: 19-year old male with febrile illness after jet ski accident

The December 2002 COM. A 19-year-old healthy male fell into stagnant water of the intercostal waterway (salt water of South Florida), following a jet ski accident. He sustained minor superficial injuries but engulfed significant quantities of water and sediment. A few days later he developed bifrontal headaches, vomiting, a stiff neck and a temperature of 102 degrees F. A CT scan on admission without contrast was negative. The CSF had markedly elevated white count but bacterial and fungal cultures were negative. He became progressively lethargic. On the fifth day he developed seizure activity. He expired the next day despite antibiotics. Gross examination of the brain at autopsy revealed edema, cerebellar tonsillar herniation and purulent meningitis. Microscopic examination revealed a massive leptomeningeal inflammatory infiltrate composed of neutrophils, lymphocytes, and numerous histiocyte-like cells. The inflammatory infiltrate extended into the cerebral parenchyma in numerous areas also involving the cerebellum, brainstem and ventricular system. Given the exposure to stagnant water (later confirmed to be a man-made fresh water lake), and the numerous histiocytic-like cells, suspicion for an amebic etiology of the disease process was raised and the CDC identified the ameba as Naegleria Fowleri. Infection by Naegleria Fowleri, a free-living ameba, occurs after exposure to polluted water in man-made fresh water lakes, ponds, swimming pools, particularly during the warm weather months when the thermophilic ameba grows well. The pathologic substrate of the infection is an acute hemorrhagic, necrotizing meningo-encephalitis mainly at the base of the brain, brainstem and cerebellum occurring in young, healthy individuals.

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.

Elimination of free-living amoebae in fresh water with pulsed electric fields

This study investigates the effects of pulsed electric fields on the inactivation of trophozoite form of Naegleria lovaniensis Ar9M-1 in batch and flow processes, systematically examining the lethal effect of field strength, pulse duration, number of pulses, and pulse frequency. Our results show that amoebae eradication is modulated by pulse parameters, composition of the pulsing medium, and physiological state of the cells. Cell survival is not related to the energy delivered to the cell suspension during the electrical treatment. For a given energy a strong field applied for a short cumulative pulse duration affects viability more than a weak field with a long cumulative pulsation. We also determine the optimal electrical conditions to obtain an inactivation rate higher than 95% while using the least energy. Flow processes allow to treat large-scale volumes. Our results show that the most efficient flow process for amoeba eradication requires a field parallel to the flow. Pulsed electric fields are a new and attractive method for inactivating amoebae in large volumes of fresh water.

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.

Development of 18S rRNA-targeted oligonucleotide probes for specific detection of Hartmannella and Naegleria in Legionella-positive environmental samples

Aquatic protozoa are natural hosts of the human pathogen Legionella pneumophila. The fluorescence labeled 16S rRNA-targeted oligonucleotide probe LEGPNE1 has recently been shown to specifically detect extracellular legionellae as well as intracellular legionellae parasitizing protozoa. In this study we designed oligonucleotide probes which are complementary to distinct regions of the 18S rRNA of the Legionella host organisms of the genera Hartmannella and Naegleria. The specificity of the probes, HART498 and NAEG1088, was tested by in situ hybridization of various laboratory reference strains. In order to evaluate the fluorescent probes for environmental studies three selected Legionella-positive cold water habitats were examined for the presence of these protozoa. Traditional culture methods followed by morphological identification revealed an almost consistent presence of Naegleria spp. in cold water habitats. Other protozoa species including Acanthamoeba spp., Echinamoeba spp., Hartmannella spp., Platyamoeba placida, Saccamoeba spp., Thecamoeba quadrilineata, and Vexillifera spp. were found sporadically. Concomitant analysis of the pH, conductivity and temperature of the water samples revealed no preference of Legionella or the respective protozoa for certain environmental conditions. The specificity of the newly designed 18S rRNA probes demonstrates that they are valuable and rapid tools for the identification of culturable environmental protozoa.

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.

Non-Acanthamoeba amebic keratitis

PURPOSE

To describe the clinical presentation and outcome of two cases with presumed non-Acanthamoeba amebic keratitis.

METHODS

Case reports.

RESULTS

Both patients presented with typical symptoms and signs of Acanthamoeba keratitis. The patients' soft contact lenses, lens cases, open solutions, and conjunctival samples were cultured. Diagnosis of non-Acanthamoeba amebic keratitis was based on the presence of keratitis and amebic growth from patients' contact lenses of the affected eyes. Amebic culture from the contralateral contact lens was negative. Vahlkampfia cysts were identified in case 1, and Naegleria cysts in case 2. Topical treatment with polyhexamethylene biguanide and propamidine resolved the keratitis in case 1. Case 2 was lost to follow-up.

CONCLUSION

Non-Acanthamoeba amebic keratitis was diagnosed in two patients based on the clinical presentation (resembling Acanthamoeba keratitis), culture of the contact lens, and response to antiamebic treatment (in one case). Keratitis associated with Naegleria contamination of contact lenses has not been previously reported.

Comparison of free-living amoebae in hot water systems of hospitals with isolates from moist sanitary areas by identifying genera and determining temperature tolerance

Legionella-contaminated hot water systems and moist sanitary areas in six hospitals were sampled for amoebae by following a standardized collection protocol. Genus identifications and temperature tolerance determinations were made. Amoebae identified as Hartmannella vermiformis (65%), Echinamoebae spp. (15%), Saccamoebae spp. (12%), and Vahlkampfia spp. (9%) were detected in 29 of 56 (52%) hot water samples. Twenty-three of 49 (47%) swabs obtained from moist areas were amoeba positive. The following genera were identified: Acanthamoeba (22%), Naegleria (22%), Vahlkampfia (20%), Hartmannella (15%), and Vanella (7%). The temperature tolerance of amoebae from hot water systems was strikingly different from that of amoebae from moist areas. At 44 degrees C on agar, 59% of amoebic isolates sampled from hot water systems showed growth. The corresponding value for isolates from moist areas was only 17%. Six Acanthamoeba isolates from the moist areas were considered potential pathogens. Four Hartmannella and two Saccamoeba isolates from hot water could be cultured at 53 degrees C.

Isolation, identification and increasing importance of 'free-living' amoebae causing human disease

Amphizoic small amoebic protozoa are capable of existing both in 'free-living' and in 'parasitic' form depending on the actual conditions. Two genera (Naegleria and Acanthamoeba) have become recognised as opportunist human parasites. Since the first description in 1965 of a lethal case of primary amoebic meningoencephalitis (PAM) caused by Naegleria, many more (mostly lethal) cases have been reported, while granulomatous amoebic encephalitis (GAE), as well as eye (keratinitis, conjunctivitis, etc.), ear, nose, skin and internal organ infections caused by Acanthamoeba have also occurred in rapidly increasing numbers. Both pathogenic and non-pathogenic species of Naegleria and Acanthamoeba are found worldwide in water, soil and dust, where they provide a potential source of infection. Successful differential diagnosis and appropriate (specific) therapy depends on precise laboratory identification of the 'free-living' amoebae. In most cases, isolation from the environment can be achieved, but identification and differentiation of the pathogenic and non-pathogenic strains is not easy. The methods presently available do not fulfil completely the requirements for specificity, sensitivity and reliability. Morphological criteria are inadequate, while thermophilic character, pH dependency and even virulence in infected mice, are not unambiguous features of pathogenicity of the different strains. More promising are molecular methods, such as restriction endonuclease digestion of whole-cell DNA or mitochondrial DNA, as well as iso-enzyme profile analysis after iso-electric focusing and staining for acid phosphatase and propionyl esterase activity. Use of appropriate monoclonal antibodies has also yielded promising results in the differentiation of human pathogenic and non-pathogenic strains. However, quicker, simpler, more specific and reliable methods are still highly desirable. The significance of endosymbiosis (especially with Legionella strains) is not well understood. The results of a systematic survey in Hungary for the isolation and identification of 'free-living' amoebae, including an investigation of the Hungarian amoebic fauna, the isolation of possibly pathogenic Naegleria strains and of some Acanthamoeba strains from eye diseases, as well as the finding of a case of endosymbiosis, are also reported here.

Techniques for isolating thermotolerant and pathogenic freeliving amebae

Several conditions of isolation were evaluated to determine which yielded the greatest number of thermotolerant and pathogenic freeliving amebae. Swab samples, easier to obtain and process, produced more pathogenic amebae than water samples. If water samples are required, 50-ml volumes gave the greatest percentage of pathogenic isolates. An incubating temperature of 42 degrees C yielded the most thermotolerant amebae. A total of 11 pathogenic isolates were obtained from 762 environmental samples and were Acanthamoeba (55%), Naegleria fowleri Carter, 1970 (27%), and N. australiensis De Jonckheere, 1981 (18%).

[Acanthamoeba, naturally intracellularly infected with Pseudomonas aeruginosa, after their isolation from a microbiologically contaminated drinking water system in a hospital]

The drinking water system of a new hospital building that was highly contaminated with bacteria before opening was investigated too for the prevalence of small free living amoebae. Germ counts resulted in > 100 CFU/ml in 100% of the cold water samples, that showed also growth of P. aeruginosa, whereas E. coli and coliforme bacteria could not be identified. The investigation of 37 water samples for protozoa revealed growth of small freeliving amoebae in 20 samples (54%) belonging to 10 species of the genus Acanthamoeba, Naegleria, Hartmannella, Echinamoeba among others. In addition 2 Ciliate- and 2 Microflagellate-species could be observed. While all Naegleria strains isolated belonged to the N. gruberi-complex two of 16 Acanthamoeba-isolates proved to be pathogenic for laboratory mice. From 7 watersamples positive with P. aeruginosa 5 Acanthamoeba- and 2 Echinamoeba strains could be isolated which revealed intracellular multiplication of P. aeruginosa. Because of their well known resistances against chlorine, the amoebae and their cysts are considered to be vectors for these intracellular bacteria. A complete sanitation of the incriminated drinking water system was accomplished by combined chemical and thermic disinfection measures.

Isolation and identification of free-living amoebae from some water sources in Alexandria

Samples from different water sources of Alexandria, and from nasal passages of 500 healthy children inhabiting areas nearby these sources were examined for the presence of free-living amoebae. These samples were cultured on 1.5% non nutrient agar streaked with bacteria. Amoebae were isolated and identified by means of their morphological characters and ability to produce flagellated forms. Characteristics of the cystic stages and pattern of excystation also aided in the identification of the various species. Nine species, Naegleria gruberi, N. fowleri, Acanthamoeba rhysodes, A. glebae, A. culbertsoni, A. astronyxis, A. palestinensis, V. avara and V. inornata were isolated from the water of canals and drains. N. gruberi and A. rhysodes were found in the nasal passages of six healthy children living near the contaminated canals. No amoebae were encountered in the drinking water, swimming pools, sea and lake water included in this study.

Successful treatment of primary amebic meningoencephalitis

The fourth documented survivor of primary amebic meningoencephalitis, a young man with a history of waterskiing in a stagnant freshwater lake in northeastern Pennsylvania, is presented. Early consideration of this unusual diagnosis, based on historical factors (recent contact with warm fresh water), coupled with prompt aggressive therapy with high-dose amphotericin B is emphasized in achieving a successful outcome.

Amplification of repetitive DNA for the specific detection of Naegleria fowleri

By using hybridization at low C0t values, a genomic library on Naegleria fowleri was screened for clones containing repetitive DNA. Partial sequence information from a repetitive clone, Nf9, showed sequence homologies with the mitochondrial ATPase 6 subunit from yeasts and other organisms. Synthetic DNA primers were selected and tested in amplification reactions. Nonstringent hybridization conditions were defined which allowed amplification of N. fowleri DNA and reduced amplification of DNA from nonpathogenic Naegleria species. Stringent conditions were selected which allowed detection only of N. fowleri. Identity of the amplified DNA was confirmed by using internal restriction sites and an internal primer. In a blind study, tissue from mice experimentally infected with N. fowleri was specifically detected by using stringent hybridization conditions.

Differentiation of Naegleria fowleri from Acanthamoeba species by using monoclonal antibodies and flow cytometry

Monoclonal antibodies to Naegleria fowleri and Acanthamoeba polyphaga were analyzed by enzyme-linked immunosorbent assay, indirect immunofluorescence microscopy, and fluorescence flow cytometry to assess specificity and cross-reactivity with axenically cultured N. fowleri and Acanthamoeba spp. Four monoclonal antibodies to N. fowleri were specific for N. fowleri and had no reactivity to A. polyphaga. Similarly, four monoclonal antibodies to A. polyphaga did not react with N. fowleri. Two of the four monoclonal antibodies to A. polyphaga did not react with other Acanthamoeba spp. tested, while two of the antibodies demonstrated a high degree of cross-reactivity with a putative Acanthamoeba castellanii strain by immunofluorescence microscopy; this was confirmed by fluorescence flow cytometry for one of the antibodies. These monoclonal antibodies were used to identify Acanthamoeba trophozoites in infected brain sections of a patient who died of suspected Acanthamoeba-caused granulomatous amoebic encephalitis, demonstrating potential utility in the direct identification of N. fowleri and Acanthamoeba spp. in clinical specimens.

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.

[Primary amebic meningoencephalitis caused by Naegleria fowleri in an adolescent from Huetamo, Michoacan, Mexico]

A 13 year old boy died after a three day illness with severe headache, explosive vomiting, fever and progressive loss of consciousness. The autopsy revealed purulent and necrotizing meningoencephalitis mainly involving the basal regions and posterior fossa and on microscopic examination numerous trophozoites of Naegleria were seen in the meninges and necrotic brain tissue. The trophozoites were identified as Naegleria fowleri by immunoperoxidase staining. This case as well as others previously reported in Mexico and the documented presence of Naegleria species from several sources indicate that primary amebic meningoencephalitis should be considered in the differential diagnosis of cases with neurological symptoms of sudden onset.

Nasal carriage of Naegleria fowleri and its environmental occurrence in Borno State, Nigeria

The presence of free living amoebae was investigated in the nasal passages of 50 healthy children and in environmental sources in Maiduguri, Borno State of Nigeria. Three of the children yielded positive cultures of Naegleria fowleri. All the five water samples and two of the nine soil samples examined from different localities were positive for N. fowleri. The isolates proved pathogenic for laboratory mice causing a fatal meningoencephalitis. The epidemiological significance of the findings is discussed.