Cytopathogenicity of Naegleria fowleri for cultured rat neuroblastoma cells

The cytopathogenicity of Naegleria fowleri strain LEE (ATCC-30894) for cultured rat neuroblastoma cells (B-103) has been investigated. Both live N. fowleri amoebae and Naegleria lysates added to 51Cr-labeled B-103 cells caused release of radiolabel, which was dependent upon the ratio of amoebae to target cells or to the lysate concentration. Lysates of N. fowleri strains LEE, NF-66, NF-69, and HB-4 were equally injurious to B-103 target cells whereas lysates of strains 6088 and KUL were less cytotoxic. Highly pathogenic mouse-passaged strain LEE were less cytotoxic than axenically grown amoebae. Maximum cytotoxicity was observed in lysates from amoebae in late exponential or early stationary phase of growth. Cytopathogenicity of lysates was reduced after heating at 44 degrees C for 60 min or at 60 degrees C for 30 min. Cytotoxicity was stable during storage at 4 degrees C or at -20 degrees C for 26 h. Neither live amoebae nor lysates injured B-103 target cells at 4 degrees C. Live amoebae and lysates injured B-103 by a time, temperature, and concentration dependent process.

Differentiation in Acanthamoeba castellanii is induced by specific monoclonal antibodies

Monoclonal antibodies that bind a large molecular weight plasma membrane protein of Acanthamoeba castellanii cause the cells to differentiate. A different monoclonal antibody that binds specifically to the major plasma membrane protein has no effect upon cell division or differentiation. The induction of differentiation by the monoclonal antibodies requires a bivalent attachment, more than a single binding cycle of the antibody to the plasma membrane protein, does not require cell-cell contact, and appears to be mediated by an inhibition of pinocytosis. These results suggest one of two alternatives: either this free living amoeba possesses a cell surface receptor that serves to initiate the differentiation process when stimulated, or the specific plasma membrane antigen for the differentiation-inducing monoclonal antibodies is an essential component of the pinocytotic mechanism. While it seems more likely on the basis of available evidence that we are observing the biological effects of a cell surface receptor, either of the two alternative circumstances open up investigative areas of large significance.

Toxicity of ricin, diphtheria toxin and alpha-Amanitin for Acanthamoeba castellanii (1983)

Selective cytotoxic agents, highly specific antibody coupled to potent toxin molecules, could, theoretically, be useful in the treatment of protozoan infections. To examine this possibility we began to synthesize immunotoxins for a model protozoan system, Acanthamoeba castellanii. We report here the selection of a suitable toxic moiety for this system. alpha-Amanitin was toxic for the amoeba, effecting a 50% decrease in in vivo protein synthesis at approximately 20 microM. However, the chemical modification of alpha-amanitin necessary for its covalent attachment to antibody molecules reduced A. castellanii toxicity to the extent that alpha-amanitin is unsuitable as a toxic moiety in the synthesis of A. castellanii immunotoxins. Ricin and diphtheria toxin were non-toxic for the amoeba. In addition, A. castellanii cell-free protein biosynthesis, unlike that of any other eukaryotic system examined to date, was resistant to inhibition by ricin A chain. However, diphtheria toxin A chain inhibited A. castellanii cell-free protein synthesis by 50% at 2.5 nM. The inhibition of diphtheria toxin was NAD+ dependent, suggesting that ADP-ribosylation of EF-2 could be the cause of the inhibition as it is in mammalian cell lines. The toxicity of diphtheria toxin A chain is sufficient for its use in the synthesis of immunotoxins for A. castellanii.

In vitro evidence that eukaryotic ribosomal RNA transcription is regulated by modification of RNA polymerase I

We have utilized a cell-free transcription system from Acanthamoeba castellanii to test the functional activity of RNA polymerase I and transcription initiation factor I (TIF-I) during developmental down regulation of rRNA transcription. The results strongly suggest that rRNA transcription is regulated by modification, probably covalent, of RNA polymerase I: (1) The level of activity of TIF-I in extracts from transcriptionally active and inactive cells is constant. (2) The number of RNA polymerase I molecules in transcriptionally active and inactive cells is also constant. (3) In contrast, though the specific activity of polymerase I on damaged templates remains constant, both crude and purified polymerase I from inactive cells have lost the ability to participate in faithful initiation of rRNA transcription. (4) Polymerase I purified from transcriptionally active cells has the same subunit architecture as enzyme from inactive cells. However, the latter is heat denatured 5 times faster than the active polymerase.

Viability of pathogenic and nonpathogenic free-living amoebae in long-term storage at a range of temperatures

The long-term storage of pathogenic and nonpathogenic strains of both Naegleria and Acanthamoeba spp. were tested on Page amoeba saline agar slopes for 24 months at room temperature and for 8 months at -10, 4, 10, and 15 degrees C. Acanthamoeba strains showed better survival potential than Naegleria strains, particularly when they were stored at temperatures equal to or lower than room temperature.

Synthesis and assembly of the cytoskeleton of Naegleria gruberi flagellates

When Naegleria gruberi flagellates were extracted with nonionic detergent and stained by the indirect immunofluorescence method with AA-4.3 (a monoclonal antibody against Naegleria beta-tubulin), flagella and a network of cytoskeletal microtubules (CSMT) were seen. When Naegleria amebae were examined in the same way, no cytoplasmic tubulin-containing structures were seen. Formation of the flagellate cytoskeleton was followed during the differentiation of amebae into flagellates by staining cells with AA-4.3. The first tubulin containing structures were a few cytoplasmic microtubules that formed at the time amebae rounded up into spherical cells. The formation of these microtubules was followed by the appearance of basal bodies and flagella and then by the formation of the CSMT. The CSMT formed before the cells assumed the flagellate shape. In flagellate shaped cells the CSMT radiate from the base of the flagella and follow a curving path the full length of the cell. Protein synthetic requirements for the formation of CSMT were examined by transferring cells to cycloheximide at various times after initiation. One-half the population completed the protein synthesis essential for formation of CSMT 61 min after initiation of the differentiation. This is 10 min after the time when protein synthesis for formation of flagella is completed and 10-15 min before the time when the protein synthesis necessary for formation of the flagellate shape is completed.

Phenothiazine compounds inhibit in vitro growth of pathogenic free-living amoebae

The phenothiazine compounds trifluoperazine dihydrochloride and chlorpromazine hydrochloride have in vitro activity against the pathogenic free-living amoebae Naegleria fowleri, Acanthamoeba culbertsoni, and Acanthamoeba polyphaga. Drug concentrations of 10 microM were amoebastatic; concentrations of 50 microM were either amoebastatic or amoebicidal. Concentrations of 100 microM were generally amoebicidal. The mechanism of drug action is unclear. It may reflect sensitivity of amoeba calcium regulatory protein to the phenothiazine compounds or may be due to the lipophilic action of the drugs on the amoeba plasma membrane. Accumulation of these drugs in the central nervous system makes them potentially useful chemotherapeutic agents in humans for treatment of amoebic meningoencephalitis caused by N. fowleri and Acanthamoeba spp.

Inactivation of Naegleria gruberi cysts by chlorinated cyanurates

The resistance of Naegleria gruberi cysts to chlorine in the presence of cyanuric acid was compared at pH 5 and 7. An amperometric membrane electrode was used to measure HOCl concentrations independently of the chlorinated cyanurate species, thus permitting an analysis of the role of free chlorine versus chlorinated cyanurates in cyst inactivation. In the presence of cyanuric acid, the products of the HOCl residual and the contact time required for 99% cyst inactivation were 8.5 mg . min/liter and 13.9 mg . min/liter at pH 5 and 7, respectively. The Watson's Law coefficients of dilution (n) were 1.3 and 1.6 at pH 5 and 7, respectively. The results strongly suggest that HOCl is the predominant cysticide with no measurable cysticidal effect of the chlorinated cyanurate species.

Calcium regulation of flagellation in Naegleria gruberi

The amoeba-to-flagellate transformation of Naegleria gruberi was studied, exploring the role of calcium in control of this pattern of morphogenesis. A direct and an indirect role for calcium are postulated based on experimental results. Direct inhibition in the presence of calcium is caused by ionophore A23187, substances with ionophore-like activity (amphotericin) and the hormone calcitonin, which facilitate calcium uptake into the cytosol. The indirect role is difficult to assess, but is believed to be related to calcium regulatory protein and its control of cyclic nucleotide levels in the cell, based on inhibition by trifluoperazine. Calcium flux was studied by addition of 45Ca2+ to cell cultures, and tracing its movement during the transformation period. Ultrastructural localization of calcium was attempted in amoeboid and flagellate stages, as well as in reverting flagellates. Deposits that might represent calcium were observed under the plasma membrane and, in calcium-induced reversion, in electron-dense spheres seen in the cytoplasm and at sub-membrane locations, suggesting expulsion of excess calcium.

Defined minimal growth medium for Acanthamoeba polyphaga

Nutritional requirements of Acanthamoeba polyphaga (strain PD) were compared to those reported for A. castellanii. Although A. polyphaga and A. castellanii have essentially the same minimal amino acid requirements--arginine, methionine, leucine, isoleucine, and valine--A. polyphaga cannot utilize acetate as sole carbon source, but A. castellanii can if the medium is supplemented with glycine.

Comparison of Naegleria fowleri and Naegleria gruberi cultivated in the same nutrient medium

The human pathogenic amoeboflagellate Naegleria fowleri and the nonpathogenic species N. gruberi can be cultivated axenically but usually in different media. Naegleria fowleri 6088 has been adapted to grow in Balamuth H-4 medium, usually used to propagate N. gruberi nB81, and nB81 has been adapted to grow in supplemented Nelson's medium, usually used to propagate N. fowleri. N. gruberi nB81, grown in either medium, enflagellated 135 to 150 min after subculture to non-nutrient amoeba saline, whereas 6088 required 225 min. Naegleria gruberi nB81 grown in either medium was agglutinated by 100 micrograms concanavalin A/ml, whereas N. fowleri 6088 was not. Naegleria fowleri and N. gruberi grown in Nelson's medium became rounded to a greater extent upon chilling at 5 degrees C and remained rounded longer than Naegleria grown in Balamuth medium. The specificity of the surface antigens was an inherent characteristic of each species and not dependent upon the propagating medium, but Naegleria grown in Nelson's medium was agglutinated more reproducibly and more effectively by antiserum. N. gruberi was somewhat more resistant to acriflavine, actinomycin D, cycloheximide, or tetracycline than N. fowleri, regardless of the culture medium. Naegleria fowleri 6088 grown in Nelson's medium, however, was more resistant to actinomycin D, daunomycin, mithramycin, sulfamethoxazole, or tyrocidine than 6088 grown in Balamuth medium. There are limitations on the validity of comparisons of N. fowleri and N. gruberi based upon cultures grown in different media.

Chemically defined media for the cultivation of Naegleria: pathogenic and high temperature tolerant species

Chemically defined minimal media for the cultivation of high temperature tolerant and pathogenic Naegleria spp. have been developed. A defined minimal medium, identical for N. fowleri and N. lovaniensis, consists of eleven amino acids (arginine, glycine, histidine, isoleucine, leucine, methionine, phenylalanine, proline, threonine, tryptophan, and valine), six vitamins (biotin, folic acid, hemin, pyridoxal, riboflavin, and thiamine), guanosine, glucose, salts, and metals. Three of the four strains of Naegleria fowleri tested (ATCC 30100, ATCC 30863, and ATCC 30896) and two strains of N. lovaniensis (ATCC 30467 and ATCC 30569) could be cultured beyond ten subcultures on this medium. For N. fowleri ATCC 30894 diaminopimelic acid, or lysine, or glutamic acid was also required. Mean generation time was reduced and population density increased for all strains with the introduction of glutamic acid. Glucose could be eliminated from the minimal medium only if glutamic acid was present. Without glucose, mean generation time increased and population density decreased. Diaminopimelic acid could substitute for lysin for ATCC 30894, indicating that Naegleria species may synthesize their lysine via the DAP pathway. Naegleria fowleri ATCC 30100 could be adapted to grow without serine or glycine in the minimal medium with glutamic acid added, but with mean generation time increased and population density decreased. The strain could be grown in the minimal medium in the absence of metals. For growth of N. australiensis ATCC 30958, modification of the medium by increasing metals ten-fold, substituting guanine for guanosine and adding lysine, glutamic acid, and six vitamins (p-aminobenzoic acid, choline chloride, inositol, vitamin B12, nicotinamide, and Ca pantothenate) was required.

Occurrence and pathogenicity of Naegleria fowleri in artificially heated waters

The occurrence of pathogenic Naegleria fowleri in thermal discharges, recipient waters, and cooling towers of eight power plants located in western Pennsylvania was investigated for 2 years in conjunction with several environmental measurements. Pathogenic N. fowleri was detected in one cooling tower and in the discharge, receiving waters, or both of five of eight localities. The occurrence of this organism was related to elevated temperatures, but no significant correlation was found for other biological and chemical parameters. Laboratory experiments on the effect of pH on pathogenic N. fowleri documented 100% survival at a range from 2.1 to 8.15. Higher pH reduced or killed the amoebae. No case of human primary amoebic meningoencephalitis occurred during the study.

Inhibition of Naegleria fowleri by microbial iron-chelating agents: ecological implications

Deferrioxamine B and rhodotorulic acid, iron-chelating agents of microbial origin, exerted a pronounced inhibitory effect on pathogenic Naegleria fowleri at microgram levels. This inhibition was diminished by adding iron to the chelators before incubation with Naegleria isolates. These and related microbial iron chelators occur naturally in the environment. This could be of considerable ecological significance and provides a novel hypothesis to account for the proliferation of pathogenic Naegleria spp. in certain aquatic habitats.

Site of expression of immunity to Naegleria fowleri in immunized mice

An experiment was performed which confirmed a previous finding that mice are protected against Naegleria fowleri infection by immunization with amoeba-free supernatant from amoeba cultures. Histological observations suggested that this protection is expressed mainly at the nasal mucosa and possibly results from the combined effects of polymorphonuclear leucocyte-mediated killing of the amoeba and mechanical elimination of the organisms by extensive shedding of necrotic epithelium.

Application of flow cytometry to studies of pathogenic free-living amoebae

Species of small, free-living amoebae of the genera Naegleria and Acanthamoeba can cause fatal amoebic meningoencephalitis. Previous investigations have shown that pathogenic amoebae are associated with thermally altered water. Flow cytometric techniques for identifying species of pathogenic and nonpathogenic amoebae from such water have been developed, using immunofluorescence and fluorescein-bound concanavalin A. Flow cytometry is accomplished with a cytofluorograph, in which cells are dispersed in a suspended carrier liquid and passed in front of a focused argon ion laser beam. Cells are then distinguished by the degree of scattered light (size) or fluorescence. Flow cytometry techniques have proven efficient for environmental samples, as indicated by the identification of pathogenic Naegleria fowleri and nonpathogenic Naegleri gruberi and Acanthamoeba castellanii isolated from the Savannah River Plant in South Carolina. Cytofluorographic analysis of environmental samples has several advantages over the current methods of isolation and classification of free-living amoebae. With this system, it is possible to rapidly identify species and quantitate mixtures of pathogenic amoebae in environmental samples. Cytofluorographic analysis of amoebic isolates reduces the time presently required to screen environmental sites for pathogenic amoebae. The cytofluorograph permits detection and species identification of nonthermophilic Naegleria spp. and Acanthamoeba spp. that could not easily be isolated for species identification by conventional methods. Other advantages of flow cytometry over fluorescent microscopy include a high degree of statistical precision due to the large numbers measured, high immunofluorescent titers, and elimination of subjectivity and fluorescence fading.

Biological factors affecting enflagellation of Naegleria fowleri

Naegleria fowleri is a pathogenic amoeboflagellate that can be evoked to transform from amoebae to flagellates by subculture to nonnutrient buffer. More than half of the amoebae of strains KUL, nN68, and Lovell became enflagellated 300 min after subculture to amoeba-saline, whereas no amoebae of strains NF66, NF69, and HB4 did. N. fowleri nN68 enflagellated best when grown at 32 or 37 degrees C and subcultured to amoeba-saline at 37 or 42 degrees C. Amoebae from the stationary phase of growth enflagellated more readily than did actively growing amoebae. Incubation in expended culture medium from stationary-phase cultures enhanced the capability of growing amoebae to enflagellate after subculture to amoebasaline. Enflagellation was more extensive when the population density in amoebasaline did not exceed 2 x 10(5) amoebae per ml. Cycloheximide at 1 microgram/ml and actinomycin D at 25 micrograms/ml inhibited growth of N. fowleri nN68. Cycloheximide at 0.5 microgram/ml and actinomycin D at 25 micrograms/ml completely prevented enflagellation when added at time zero. Cycloheximide at 0.5 microgram/ml, added 120 to 300 min after initiation of enflagellation, prevented further differentiation and caused existing flagellates to revert to amoeboid cells. Similarly, actinomycin D at 25 micrograms/ml, added 90 to 300 min after initiation of enflagellation, retarded differentiation and caused flagellates to revert. Radiolabeled precursors were incorporated into macromolecules during differentiation in nonnutrient buffer. Enflagellation of N. fowleri is a suitable model for studying regulation of a eucaryotic protist.

[Isolation of free-living amoebas from bottled mineral water]

Foram isoladas amebas dos gêneros Vahlkampfia, Glaeseria, Acanthamoeba, Filamoeba, Amoeba, Platyamoeba e Hartmanella de dez diferentes marcas de água mineral engarrafadas, servidas no Rio de Janeiro, RJ (Brasil). Somente uma das marcas foi negativa para protozoários, enquanto que de todas as outras foram isoladas amebas de vida livre. O significado desses resultados é discutido como um indicador de qualidade da água mineral usada comercialmente, destacando-se o fato de que alguns desses microorganismos são potencialmente patogênicos.

Cocultivation of Legionella pneumophila and free-living amoebae

Studies of the interaction of Legionella pneumophila with free-living amoebae showed that Naegleria lovaniensis and Acanthamoeba royreba could use L. pneumophila as a sole food source. However, growth of the amoebae on nonnutrient agar plates seeded with L. pneumophila was slower than growth on nonnutrient agar plates seeded with Escherichia coli. On inoculation of L. pneumophila into axenic cultures of N. lovaniensis and A. royreba, 99.9% of the L. pneumophila was destroyed within 24 h. After several weeks, however, some amoeba cultures became chronically infected and supported the growth of L. pneumophila. Amoebae exposed to L. pneumophila and containing adhered L. pneumophila, L. pneumophila antigens, or both, showed no increased pathogenic potential on intranasal inoculation of weanling mice. Similarly, L. pneumophila propagated in chronically infected amoeba cultures showed no increase in virulence on intraperitoneal inoculation of guinea pigs relative to L. pneumophila grown in yeast extract broth.

The fine structure of Acanthamoeba astronyxis, with special emphasis on encystment

The fine structure of the trophozoite, encysting cells, and the cyst of Acanthamoeba astronyxis has been examined. In the trophic form a microtubule organizing center was associated with a well developed Golgi complex. During encystment the organelles of the amoeba changed considerably. The profiles of rough endoplasmic reticulum elongated and were often arranged in circles of multilayered concentric systems, enclosing mitochondria, the nucleus, or other inclusions. The mitochondria showed a tendency toward elongation and constriction. One or two nucleolus-like bodies appeared in the nucleus. Lipid droplets increased considerably in amount and were distributed individually or as aggregates. The mature cyst was star-shaped and surrounded by an almost circular exocyst and an endocyst that was closely apposed to the cell membrane. Both walls differed in their thickness and granulation. The exocyst was continuous over the entire cyst, while the endocyst was interrupted by gaps, ostioles, in the region of the rays. Within the ostioles was a bell-shaped structure, the operculum. The latter was composed of a granular material comparable in electron density to that of the endocyst.

Characterization of proteins in flagellates and growing amebae of Naegleria fowleri

Polypeptides of whole-cell extracts of Naegleria fowleri flagellates and growing amebae were resolved by two-dimensional polyacrylamide gel electrophoresis. Autoradiograms of the [35S]methionine-labeled polypeptides of amebae and flagellates were analyzed by two dimensional densitometry to determine whether there were correlations between intracellular concentration of a protein and subunit size or charge. The majority of the polypeptides of amebae and flagellates had molecular sizes in the range of 20 to 60 kilodaltons. The radioactivity per polypeptide species in the size range of 20 to 60 kilodaltons was greater in amebae than in flagellates. The greatest number of polypeptides detected in amebae and flagellates was in the isoelectric focusing range of pH 6 to 7. The radioactivity per polypeptide species in the isoelectric focusing gradient below 6.3 was greater in amebae than in flagellates. Polypeptides in the size range of 20 to 60 kilodaltons had a median isoelectric point below pI 6.3, whereas those larger than 60 kilodaltons had a median pI value above 6.3. These data indicated that molecular size and charge were not entirely independent variables and that the size and charge of a polypeptide might have an important influence in determining its intracellular concentration in both amebae and flagellates. Autoradiograms were also compared so that changes in intracellular protein complement and concentrations occurring during differentiation could be recognized. The relative amounts of a limited number of polypeptides increased markedly, and others decreased markedly, during enflagellation.

Temperature-compensated oscillations in respiration and cellular protein content in synchronous cultures of Acanthamoeba castellanii

Synchronous cultures of the soil amoeba Acanthamoeba castellanii, established by a selection procedure, show significant oscillations of respiration and total cell protein. There was little difference between the period of these oscillations, which averaged 76 min, although the five incubation temperatures used varied between 20 degrees C and 30 degrees C and the cell division time increased from 7.8 to 16 hr. The phase of these oscillations also corresponded approximately at all incubation temperatures. Similar observations made over the whole division cycle at three temperatures indicated that similar oscillations occurred, with a constant period of 65 min, although these data were too variable to show this unequivocally. Control (asynchronous) cultures show that the oscillations are not a consequence of metabolic perturbation produced by the centrifugal selection procedure. It is suggested that these temperature-compensated epigenetic oscillations serve a dual role in cell cycle and circadian timekeeping and that cell cycle time is quantized.

Cytopathogenicity of Naegleria gruberi for rat neuroblastoma cell cultures

Amoebae of Naegleria gruberi were cytopathic for cultures of rat neuroblastoma (B-103) cells. N. gruberi grew and destroyed B-103 cells at 30 degrees C. As few as one amoeba inoculated per million B-103 cells resulted in cytopathogenicity after extensive growth of N. gruberi.

DNA synthesis during growth and synchronous differentiation of Naegleria

Naegleria gruberi amoebae were stimulated to differentiate synchronously into flagellates under growth conditions by lowering the temperature from 32 degrees C to 20.5 degrees C. In the presence of nutrient medium, flagellates will eventually revert to amoebae and resume growth. The time course of nuclear DNA synthesis, using a double thymidine isotope procedure, was determined for: (1) logarithmically growing amoebae, (2) differentiating cells, and (3) flagellates that were reverting to amoebae. DNA replication ceased 10 min. after the stimulation of differentiation, and began again during reversion. Neither de novo transcription nor translation appear to be required for the cessation of DNA replication during differentiation.

Growth phase dependent alterations in the surface coat of Acanthamoeba castellanii

Application of ruthenium red, cationized ferritin and concanavalin A to exponentially growing trophozoites reveals on their plasma membrane negatively charged surface coat bearing sugar residues. In the coat of trophozoites from advanced stationary growth phase no sugar residues can be visualized. In mature cysts the external layer of their wall is negatively charged, however, on their protoplast surface no terminals reacting with the 2 polycations, or with concanavalin A can be revealed, even though the penetration of the reagents has been ensured by enzymatic impairing of the cyst wall. The results are confronted with the known facts concerning alterations of physiological properties of plasma membrane occurring during the life cycle of Acanthamoeba.

The mitochondrial adenosine triphosphatase of Acanthamoeba castellanii. Partial characterization and changes in activity during exponential growth

1. The mitochondrial adenosine triphosphatase (ATPase) of Acanthamoeba castellanii is Mg2+-requiring (optimum cation: ATP ratio of 1.5) and has two pH optima of activity (at pH 6.6 and 8.1). 2. ATPase activity of submitochondrial particles is effectively inhibited by twelve different inhibitors of energy conservation suggesting similarities in inhibitor-binding sites to other previously characterized complexes. 3. Gel filtration by passage through Sephadex G-50 increases ATPase activity of submitochondrial particles between 1.5 and 3.5 fold indicating the presence of a low molecular weight inhibitor protein. 4. After removal of the inhibitor protein, sensitivity to inhibitors of energy conservation decreases by between 1.5 and 14 fold. Crude F1-inhibitor preparations from A. castellanii, Schizosaccharomyces pombe, Tetrahymena pyriformis and bovine heart also inhibit ATPase activity. 5. Large variations in ATPase activity, F1-inhibitor protein activity, and amounts of immunologically-determined ATPase protein were observed during exponential growth, and the correlation between changes in these measurements is discussed. 6. The results are also discussed highlighting the similarities between the mitochondrial ATPase of A. castellanii and other mitochondrial ATPases.

Pathogenic and nonpathogenic Acanthamoeba spp. in thermally polluted discharges and surface waters

During spring and autumn, the total number of amoebae and the number of acanthamoeba species able to grow at 37 degrees C were determined in six thermally polluted factory discharges and the surrounding surface waters. The isolated Acanthamoeba strains were studied for growth in axenic medium, cytopathic effect in Vero cell cultures, and virulence in mice. Although more amoebae were isolated in autumn, the number of Acanthamoeba species was lower than in spring, when the percent of pathogenic strains among the isolates was highest. Higher concentrations of amoebae were found in warm discharges, and more virulent strains occurred in thermal discharges than in surface waters.

Developmental changes in the localization of calcium binding sites in Acanthamoeba castellanii

Vegetative cells of Acanthamoeba castellanii have the ability to bind calcium on the plasma membrane in form of the electron-dense deposits. The appearance of the deposits depends on the age of Acanthamoeba culture. In 24-h-old culture the deposits are very small, with diameter of 26 nm. During aging of culture, at both logarithmic and stationary growth phases, the diameter of deposits is larger (70-80 nm), while the deposits are localized only on the plasma membrane. During differentiation of Acanthamoeba cells into cysts electron-dense deposits with a diameter of about 170 nm appear in the mitochondria, whereas no deposits are observed on the plasma membrane. However, at the first stage of differentiation electron-dense material together with extruded membraneous fragments are also observed outside of some newly-formed young cysts. These results suggest that in Acanthamoeba cells, depending on the stage of life cycle, either plasma membrane or mitochondria may be involved in storage of excess cellular calcium.

Activation of the alternative complement pathway by Naegleria fowleri

Naegleria fowleri amoebae were lysed by adult fresh human serum, and their multiplication was inhibited in culture medium supplemented with 10% fresh human serum. Heat inactivation (56 degrees C, 30 min) of serum abrogated these lytic and inhibitory effects. Absorption of human serum with amoebae failed to reduce immunoglobulin levels, and no specific antibody was detected in untreated or treated sera by counterimmunoelectrophoresis. Conversion of C3 and C3i occurred after incubation of n. fowleri with serum which had been treated with ethylene glycol-bis(beta-aminoethyl ether)-N,N-tetraacetic acid, indicating activation of complement via the alternative pathway.

Effect of disinfectants on pathogenic free-living amoebae: in axenic conditions

The amoebicidal properties of chlorine, chlorine dioxide, ozone, and deciquam 222 were examined in axenic conditions. Naegleria spp. were found to be more sensitive to chlorine and chlorine dioxide than Acanthamoeba spp. No marked difference in sensitivity to ozone or deciquam 222 could be detected between the pathogenic (A-1) and nonpathogenic (1501) strains of Acanthamoeba and the pathogenic (MsT) and nonpathogenic (P1200f) strains of Naegleria. Methods of disinfection are discussed with reference to suitability of the disinfectants to real conditions.

Adenylate cyclase activity during growth and encystment of Acanthamoeba castellanii

The adenylate cyclase activity of Acanthamoeba castellanii (Neff) was studied in extracts prepared after breaking cells in the Potter-Elvehjem homogenizer. The adenylate cyclase activity of cells is low during the exponential growth phase, but then rises 2--4-fold during the stationary phase to a peak, roughly at the time that cyst forms are detectable in the culture. A 2--4-fold activity rise to a peak also occurs 4--8 h after late log cells are transferred to a non-nutrient encystment medium, a time which is shortly before numbers of cyst forms can be detected in the culture. The pattern of activity observed when stationary phase cells are transferred to encystment medium is complex and depends in part on whether the cultures have exhibited the peak of cyclase activity and have begun to initiate cyst formation prior to the transfer. Within the usual time frame after transfer to encystment medium, early logarithmic phase cells do not exhibit a 2--4-fold rise of cyclase activity and they do not encyst. The results suggest a relationship between encystment and the pattern of rise and fall in cyclase specific activity. Fractionation of the homogenate of trophozoites indicated that adenylate cyclase activity was associated with the particulate microsomal fraction.

Rapid growth of Acanthamoeba in defined media; induction of encystment by glucose-acetate starvation

Defined media are described that support 14-20 h generation times for Acanthamoeba castellanii and A. rhysodes in monolayer cultures. The media differ in minor ways from previously described media, but the growth rates are greatly improved over previously reported values. Maximum growth rates were observed for A. castellanii in a complex medium containing 21 amino acids, but near-maximum rates could be achieved in relatively simple media containing 9 amino acids. Growth occurred with 6 amino acids, as reported by others, but generation times exceeded 30 h. Amitosis was a common problem during early subcultures in defined media, defined media by glucose and acetate starvation. The rate of encystment varied with cell density at the time of starvation and was optimal at initial densities of 400-800 amebae/mm2.

Growth characteristics, cytopathic effect in cell culture, and virulence in mice of 36 type strains belonging to 19 different Acanthamoeba spp

A total of 36 strains belonging to 19 different species of Acanthamoeba were compared for temperature tolerance, ability to grow in an axenic medium, cytopathic effect in Vero cell culture, and virulence in mice. Pathogenic strains appeared to belong to different species, whereas pathogenic and nonpathogenic strains occurred in one species. Although growth at high temperatures and readiness to grow axenically indicated a potential for pathogenicity, each such strain had to be tested in cell cultures or laboratory mice to determine whether or not it was virulent. This study was not intended to differentiate Acanthamoeba spp., but to provide methods to be used for the specific isolation and identification of pathogenic Acanthamoeba strains.

Changes in transfer ribonucleic acid population of Acanthamoeba castellanii during growth and encystment

Fifteen aminoacyl-transfer ribonucleic acids (tRNA's) from vegetative cells (trophozoites) and mature cysts of Acanthamoeba castellanii were compared by reversed-phase 5 chromatography. Little or no differences were detected in reversed-phase 5 chromatography elution profiles of alanyl-, arginyl-, isoleucyl-, phenylalanyl-, prolyl-, seryl-, threonyl-, tryptophanyl- and valyl-tRNA's. Significant differences in the relative proportions of isoaccepting species of leucyl-, lysyl-, methionyl-, aspartyl-, histidyl-, and tyrosyl-tRNA's were observed. Based upon the criterion of cyanogen bromide reactivity with the modified nucleoside queuosine, the content of queuosine in aspartyl-tRNA of A, castellanii is significantly greater in mature cysts than in trophozoites. The similarity of change in reversed-phase 5 chromatography elution profiles of aspartyl-, histidyl-, and tyrosyl-tRNA suggests that a common mechanism is responsible for alterations in the chromatographic patterns.

Alternative states of Amoebae. Studies on Nuclear RNA and DNA synthesis

Actively proliferating Amoebae were kept in the interphase part of the cell cycle for prolonged periods by restricting the food supply. When the cells were returned to normal food supply, the clones failed to grow exponentially. The clones in this period of growth phase were in an 'alternative state' as opposed to their normal state of active proliferation. Nuclear RNA and DNA synthesis of cells in this alternative state was studied. Nuclei from cells in this alternative state were implanted into normal cells to study the effects on the synthesizing activities of the host cells. The results showed that there was a marked reduction in DNA and RNA synthesis in the host nucleus in the binucleated cells.

Cellular and environmental variables determining numbers of flagella in temperature-shocked Naegleria

Naegleria gruberi amebae normally transform into biflagellated cells. When subjected to high temperatures during flagellate differentiation, populations develop an average of 4-5 flagella/flagellate. Attempts to maximize this phenomenon by altering cellular and environmental variables revealed that: (a) few Naegleria isolates become multiflagellated: strain NB-1 gives the greatest response to heat shocks; (b) temperature is the most critical variable: highest numbers of flagella are obtained only if cells are temperature-shocked at precisely 38.2 +/- 0.1 C, then returned to 19-22 C to complete differentiation; (c) although pH alone does not affect numbers of flagella, a pH optimum of 5.5-7.0 exists for temperature-shocked cells; and (d) single cells in microdrops become multiflagellated, but the population response is density-dependent. Optimal conditions are described for growing, washing, and transforming amebae to generate reproducibly highest numbers of flagella.

Naegleria fowleri in chick embryos. Effects of embryo age and incubation temperature, and the infectivity of embryo-derived amebae for mice

Chick embryos were infected with Naegleria fowleri which was initially isolated from an ultimately fatal human case. Following inoculation of equivalent numbers of amebae on the chorioallantoic membrane, younger embryos died earlier than older embryos infected at the same time. Incubation of infected embryos at 32 degrees C prolonged survival only slightly in comparison with those at 37 degrees C. N. fowleri maintained for more than 25 serial passages in chick embryos retained infectivity for mice and the ability to convert to the biflagellate form in vitro.

Susceptibility of Naegleria fowleri to delta 9-tetrahydrocannabinol

Growth of the pathogenic amoeboflagellate Naegleria fowleri is inhibited by delta 9-tetrahydrocannabinol (delta 9-THC). delta 9-THC is amoebostatic at 5 to 50 micrograms/ml. delta 9-THC prevents enflagellation and encystment, but does not impair amoeboid movement. Calf serum at 10 and 20% (vol/vol) reduces the antiamoeba activity of delta 9-THC. Only 1-methoxy delta 8-tetrahydrocannabinol, of 17 cannabinoids tested, failed to inhibit growth of N. fowleri. Antinaeglerial activity was not markedly altered by opening the pyran ring, by converting the cyclohexyl ring to an aromatic ring, or by reversing the hydroxyl and pentyl groups on the benzene ring. delta 9-THC prevented the cytopathic effect of N. fowleri on African green monkey (Vero) cells and human epithelioma (HEp-2) cells in culture. delta 9-THC afforded modest protection to mice infected with N. fowleri.

The effect of inhibitors on the oxygen kinetics of terminal oxidases of Acanthamoeba castellanii

1. Respiration of growing cultures of Acanthamoeba castellanii is inhibited less than 60% by azide (35 mM); the respiration of early-exponential-phase cultures differs from that of late-exponential-phase cultures in being stimulated by up to 120% by low concentrations (less than 1 mM) of this inhibitor. Azide (0.5 mM) plus 1 mM-salicylhydroxamic acid gives 80% inhibition of respiration in early- or late-exponential-phase cultures. 2. Lineweaver-Burk plots of 1/v against 1/[O2] for growing and stationary-phase cultures give values of less than 1 muM for the apparent Km for oxygen. 3. These values are not significantly altered when determined in the presence of 1 mM-salicylhydroxamic acid. 4. Higher values (greater than 7 muM) for apparent Km values for oxygen were obtained in the presence of azide, which gives non-linear Lineweaver-Burk plots. 5. Competitive inhibition of respiration by CO occurs with Ki 2.4 muM. 6. The results are discussed in terms of the presence of three terminal oxidases in this organism, namely two oxidases with high affinities for oxygen (cytochrome c oxidase of the main phosphorylating electron-transport chain and the salicylhydroxamic acid-sensitive oxidase) and a third oxidase with a low affinity for oxygen, sensitive to inhibition by cyanide but not by azide or salicylhydroxamic acid. The relative contributions to oxygen utilization by these oxidases change during the growth of a batch culture.