[Encephalitis due to Naegleria and Acanthamoeba. Comparison of organisms and diseases (author's transl)]

Naegleria and Acanthamoeba are ubiquitous, free-living amoebas. Infections with Naegleria are acquired nasally by exposure to water and are characterized by an acute fulminant hemorrhagic necrotizing meningoencephalitis leading to death. Acanthamoeba-infections occur in chronically ill, debilitated individuals. A patchy chronic or subacute granulomatous encephalitis is produced by hematogenous spread of the amoebas. The histological or clinical diagnosis is not difficult.

[Isolation of free-living amoebae from the nasal mucosa of man. Potential risk (author's transl)]

From march 1976 until december 1978, we have analysed 1039 nasal swabs in order to discover the healthy free-living amoebae carriers. So, we have isolated 9 strains of which one Hartmannella vermiformis. From the 8 remaining Acanthamoebae, only one, ORL 561 (Acanthamoeba hatchetti) is as pathogenic for mice as the 2 other identical known strains and A. culbertsoni.

Accumulation of UDP-glucose pyrophosphorylase by axenically grown amoebae of Dictyostelium discoideum

Amoebae of the slime mould Dictyostelium discoideum AX2 possess only low UDP-glucose pyrophosphorylase activity when grown on autoclaved Klebsiella aerogenes (approx. 30 units/mg of protein), but accumulate the enzyme to approx. 150-200 units/mg of protein during vegetative growth in axenic medium. The vegetative accumulation of UDP-glucose pyrophosphorylase by axenically grown cells is prevented if autoclaved K. aerogenes are included in the axenic medium, suggesting the absence of a specific inducer. Affinity chromatography using anti-(UDP-glucose pyrophosphorylase) antibody and sodium dodecyl sulphate/polyacrylamide-gel electrophoresis indicate that the enzyme accumulated during axenic growth and that normally accumulated during development are immunologically cross-reactive and that both are composed of two subunits with mol.wts. 55,600 and 57,500 present in approximately equal amounts in the active enzyme.

The pattern of appearance of enzymic activity during the development of the Golgi apparatus in amoebae

The appearance of enzymic activity during the development of the Golgi apparatus was studied by cytochemical staining of renucleated amoebae. In cells enucleated for 4 days, there was a great decline in size and number of Golgi bodies, or dictyosomes. Subsequent renucleation by nuclear transplantation resulted in a regeneration of Golgi bodies. Samples of amoebae were fixed and incubated for cytochemical staining at intervals of 1, 6, or 24 h after renucleation. Enzymes selected for study were guanosine diphosphatase (GDPase), esterase, and thiamine pyrophosphatase (TPPase). All three were found in the Golgi apparatus of normal amoebae but they differed in their overall intracellular distribution. GDPase was normally present at the convex pole of the Golgi apparatus, in rough endoplasmic reticulum, and in the nuclear envelope. In amoebae renucleated for 1 h, light reaction product for GDPase was present throughout the small stacks of cisternae that represented the forming Golgi apparatus. By 6 h following the operation GDPase reaction product was concentrated at the convex pole of the Golgi apparatus. Esterase, which was distributed throughout the stacks of normal Golgi cisternae, displayed a similar distribution in the forming Golgi bodies as soon as they were visible. TPPase was normally present in the Golgi apparatus but was not found in the endoplasmic reticulum. In contrast to the other enzymes, TPPase reaction product was absent from the forming Golgi apparatus 1 and 6 h after renucleation, and did not appear in the Golgi apparatus until 24 h after operation. Thus, enzymes held in common between the rough endoplasmic reticulum and the Golgi apparatus were present in the forming Golgi apparatus as soon as it was detectable, but an enzyme cytochemically localized to the Golgi apparatus only appeared later in development of the organelle. It is suggested that Golgi membranes might be derived from the endoplasmic reticulum and thus immediately contain endoplasmic reticulum enzymes, while Golgi-specific enzymes are added later in development.

Mutants of Acanthamoeba castellanii resistant to erythromycin, chloramphenicol, and oligomycin

Cell lines of Acanthamoeba castellanii resistant to erythromycin (EryR), chloramphenicol (CapR), and oligomycin (OliR) have been isolated. These may be the first such mutants for A. castellanii. These mutants have been phenotypically stable for 2 years, surviving storage and vegetative multiplication in the absence of drugs. Resistance was specific for each drug, but double mutants (e.g. EryRCapR) were obtained by stepwise selection. Mutant frequencies were determined in multiwell plates; less than 10 colony forming units (CFU/10(5) amebas were observed in wild-type populations 12 days after incubation in 500 microgram Ery/ml, 2.5 mg Cap/ml, or 15 microgram Oli/ml. After 30 days, averages of 100 CFU/10(5) amebas were observed in Ery and Cap, whereas, frequencies for Oli remained unchanged. Frequencies for EryR and CapR were consistent with rates of recovery from these drugs in batch cultures. We were unable to obtain spontaneous mutants resistant to cycloheximide, emetine, 5-fluorodeoxyuridine, or ethidium bromide. EryR, CapR and OliR could be mitochondria mutants.

Observations by light microscopy on the cytopathogenicity of Naegleria fowleri in mouse embryo-cell cultures

Naegleria fowleri, strain HB-1, caused a destructive cytopathic effect (CPE) in secondary mouse-embryo (ME) cells. No evidence was found to suggest that cell-free cytotoxic factors secreted by the amoebae play a part in ME-cell destruction. In culture systems designed for the study of cytopathic factors, mammalian-cell damage seemed to occur only as a result of direct contact with active amoebae. This was confirmed when the progressive destruction of individual ME cells was observed continuously by direct microscopy and time-lapse cinemicrography. The cytoplasmic shrinkage characteristic of naegleria-induced CPE appeared to be associated with phagocytic activity of trophozoites. Adjacent ME cells remained undamaged until they themselves were physically attacked. The apparently intracellular location of amoebae seen in fixed and stained preparations was considered to be an artefact created when trophozoites and ME cells were superimposed.

The effect of antrycide of patterns of RNA synthesis in Amoeba discoides

Antrycide is an aminoquinaldine whose inhibitory action on the growth of Trypanosoma and Crithidia is not fully understood at the cellular level. The growth of Amoeba discoides in concentrations of antrycide between 0.5 and 2 microgram/ml was reduced considerably, while cells failed to divide in 4 microgram/ml. The effects on growth rate were reversible at least up until 7 days in antrycide. In order to assess the action of this synthetic drug on RNA synthesis in amoebae, the pattern of synthesis in normal cells was investigated using polyacrylamide gel electrophoresis. The profile of high molecular weight RNAs observed depended on the length of time in [3H]uridine, and was only fully developed after 66 h, when 5 peaks could be seen. The relative molecular weights of these peaks (I–V) were 2.45, 1.55, 1.13, 0.8 and 0.52 X 10(6) Daltons respectively. Those of 1.55 and 0.8 X 10(6) corresponded to ribosomal RNAs, the identity of the other peaks is unknown. After growth in 2 microgram/ml antrycide for 4 days, no high molecular weight RNA was found. Use of [14C]adenine/[3H]uridine showed that after 17 h in antrycide there was a loss of ribosomal RNA and increased levels of low molecular weight RNAs, due either to lack of synthesis or to degradation of newly synthesized material. Incorporation of [3H]leucine into hot acid-precipitable protein was inhibited in antrycide-treated cells by at least 50%. A possible explanation of the effect of antrycide on A. discoides was the inhibition of mRNA synthesis for ribosomal proteins, leading to degradation of newly synthesized rRNA. Reduced growth would continue on pre-existing ribosomes and previously synthesized long-lived mRNAs.

Resistance of pathogenic Naegleria to some common physical and chemical agents

Resistance of pathogenic Naegleria to drying, low and high temperature, and two halogens was studied. Dying made trophozoites nonviable instantaneously and cysts nonviable in less than 5 min. Trophozoites degenerated in hours at temperatures below 10 degrees C and in minutes when frozen; cysts survived according to the equation th - t0/theta 1,440/1.122T (t0 is survival at 0 degrees C; Tis temperature between 0 and 10 degrees C), but 1.5 h at --10 degrees C to 1 h at --30 degrees C. At 51, 55, 58, 63, and 65 degrees C, trophozoites survived about 30, 10, 5, 1 and less than 0.5 min, respectively, cysts survived three to four times longer at 51 degrees C and six to seven times longer at 55 to 65 degrees C. Cyst destruction rates by heat indicated first-order kinetics with 25,400 cal/1 degree C for energy of activation. Cyst destruction rates by free chlorine and I2 also conformed to first-order kinetics. Concentration-contact time curves yielded concentration coefficient values of 1.05 for free chlorine and 1.4 for I2 and point to superchlorination as an effective means of destroying the cysts if free residuals are used as a guide and allowance is provided for low temperature and/or high pH waters.

Promitosis and rod occurrence in the limax ameba Vahlkampfia lobospinosa

Nuclear division and trophozoite structure and function were investigated in Vahlkampfia lobospinosa. During karyokinesis the nucleolus remained present and divided to form polar masses. Chromatids separated and were directed to the polar masses by spindle fibers within an intact nuclear membrane. No interzonal body was formed. Trophozoites consistently contained and extruded a rod-like structure 10-15 X 1-2 micron. Although it was found in other areas of the cell within the cytoplasm, this rod most frequently protruded from the uroid.

Characteristics of the 'life spanning' phenomenon in Amoeba proteus. Independent nuclear and cytoplasmic ability to impose finite 'life span'

Amoeba proteus given adequate food grows exponentially and clones of amoebae are normally immortal. After periods of food supply restriction to that necessary for maintenance, or food intake restriction by agitation, cells subsequently given a normal growth diet produce clones of finite life span. Reciprocal nuclear transfer between maintained and normal cells demonstrated that the nucleus and cytoplasm of maintained cells have acquired the independent ability to impose a finite life span on clones developing from cells whose other components are normal. In clones developing from maintained cells, inviable cell production is enhanced and inter-division times are prolonged. Inter-division times and clones mean doubling times do not show normal distribution.

Isolation of the etiological agent of primary amoebic meningoencephalitis from artifically heated waters

To determine whether artificial heating of water by power plant discharges facilitates proliferation of the pathogenic free-living amoebae that cause primary amoebic meningoencephalitis, water samples (250 ml) were taken from discharges within 3,000 feet (ca. 914.4 m) of power plants and were processed for amoeba culture. Pathogenic Naegleria fowleri grew out of water samples from two of five lakes and rivers in Florida and from one of eight man-made lakes in Texas. Pathogenic N. fowleri did not grow from water samples taken from cooling towers and control lakes, the latter of which had no associated power plants. The identification of N. fowleri was confirmed by pathogenicity in mice and by indirect immunofluorescence analyses, by using a specific antiserum.

[The cellulase enzyme system during growth and development of Acanthamoeba castellanii (author's transl)]

It could be shown that extracts of growing cultures of Acanthamoeba castellanii contained a cellulose degrading system. Reducing sugars are split off by one component of this system at an optimum of pH 4, another enzyme changes the viscosity at an optimum of pH 6, and a third component is a beta-glucosidase with an optimum at pH 3.5. At pH 4 the cellulose degradation products are cellobiose and glucose; at pH 6 higher molecular weight oligosaccharides are produced. During the development from trophozoites to cysts in a nutrient-free medium, the activities of both cellulases decline: Prior to the start of cellulose synthesis only 30%, and in cysts only 10% of the original existing activities are detectable. The biological function of the cellulase enzyme system is discussed together with a consideration of the fact that excystment takes place without digestion of the cyst wall in which the cellulose is deposited.

Light and electron microscopic observations on encystment of Acanthamoeba palestinensis, Reich

The ultrastructural changes occurring during encystment of acanthamoeba palestinensis have been investigated. The cyst wall consists of endocyst and exocyst, both having the same fine structure. At irregular intervals in the cyst wall ostioles occupied by opercula are present. The nuclear membrane forms bulb-shaped projections and releases vesicles bounded by double membranes into the cytoplasm. Dense nucleolus-like bodies of different sizes and variable numbers are found in the nucleus of every cyst. The importance of the cyst structure as a taxonomic criterion is discussed.

Correlation of encystment and division in Schizopyrenus russelli

Schizopyrenus russelli, a free-living soil ameba, grows and encysts in the presence of bacteria. The encystment occurs with decline in the division rate. This is accompanied by incorporation of [U-14C] glucose into cyst cellulose. The degree of multiplication (but not of encystment) is a function of bacterial concentration. Berenil, a trypanocidal drug, while allowing excystment, completely inhibited multiplication of emerged amebae and their encystment. Addition of this drug after 24 hr, when amebae had gone into a phase of active division failed to check encystment, although it still inhibited further multiplication of the amebae. The findings suggest that a phase of cell division may be a prerequisite for encystment.

Cell size, macromolecular composition, and O2 consumption during agitated cultivation of Naegleria gruberi

Cell size, macromolecular composition, carbohydrate utilization patterns, and O2 concentrations were measured throughout the growth stages of Naegleria gruberi in agitated culture in a complex medium. Biphasic logarithmic growth occurred during the intial 83 hr of growth and the mean generation time was 7.0 hr and 19 hr during initial and secondary log growth stages, respectively. The maximum yield was 5 X 10(6) amebae/ml. The pH rose rapidly (1 pH unit) during the secondary log growth phase (52-83 hr) and continued into the stationary growth phase (83-120 hr). Dry weight, total protein, carbohydrate, and RNA per ameba increased just before the secondary log growth phase. RNA increase 31% to 35% per ameba at the end of each phase of log growth. DNA increased approximately 2-fold throughout the different growth phases. Average cell size increased 90% during biphasic log growth then decreased during stationary phase. O2 tension decreased from 100% to 18% of saturation during the biphasic growth phase, then increased during stationary growth to near 100% saturation. Glucose and total carbohydrate assays showed little utilization of those substrates throughout the growth stages. Naegleria gruberi presumably has a predominantly aerobic metabolism, also its metabolism may change during the different growth phases.

Cessation of nuclear DNA synthesis in differentiating Naegleria

DNA synthesis during growth and differentiation in Naegleria gruberi strain NEG populations has been studied. Autoradiography of cells labeled with [3H]thymidine revealed that grains are concentrated over the nuclei in logarithmically growing populations of cells, whereas in differentiating cells, grains are scattered over the cytoplasm; i.e. no significant nuclear labeling is detectable. It was established by MAK chromatographic analysis that [3H]thymidine is incorporated into double-stranded DNA in Naegleria and that the actual amount of incorporation in the logarithmically growing populations of cells is 20 times greater than that in differentiating cells. These results suggest that nuclear DNA synthesis is reduced markedly soon after the initiation of differentiation, while cytoplasmic DNA synthesis continues. It was established from cell cycle analysis that the approximate intervals of G1, S, G2, and M phases were 180, 183, 90, and 28 min, respectively. Hence, the reduction in the nuclear DNA synthesis in differentiating cells is not due to the inhibition of initiation of DNA replication, but rather to the termination of the DNA replicating process. Thus DNA synthesis is curtailed in the presence of RNA and protein synthesis which are required for differentiation.

Acid hydrolase activity during growth and encystment in Acanthamoeba castellanii

The activity and sedimentation of acid phosphatase (APase), acid deoxyribonuclease (DNase), and acid ribonuclease (RNase) were investigated throughout growth and encystment in Acanthamoeba castellanii. The activities/mg protein of all 3 hydrolases are high in young cultures and decrease to constant levels in postlog cells. The RNase activity/ameba decreases 50% during growth, whereas the activity/cell of both APase and DNase remains constant. The percent sedimentation at 20,000 g of all 3 enzymes gradually increases from about 40% in midlog to a plateau of 80% in postlog cells. During encystment, the sedimentation behavior of RNase differs from that of APase and DNase. Encystment is characterized by a differential decrease in the activity/cell of the 3 hydrolases, with RNase decreasing most rapidly and APase least rapidly. APase is unique in that a transient increase of its specific activity is noted during encystment, even though its activity/cell is decreasing.

Endosymbiosis in amoebae: recently established endosymbionts have become required cytoplasmic components

A strain of large, free-living amoeba that became dependent on bacterial endosymbionts which had infected the amoebae initially as intracellular parasites, was studied by micrurgy and electron microscopy. The results show that the infected host cells require the presence of live endosymbionts for their survival.Thus, the nucleus of an infected amoeba can form a viable cell with the cytoplasm of a noninfected amoeba only when live endosymbionts are present. The endosymbiotic bacteria are not digested by the host amoebae and are not themselves used as nutritional supplement. While the host amoebae are dependent specifically on the endosymbionts, the latter can live inside amoebae of different strains, indicating that their dependence on the host cells is not yet strain specific.

Effect of glucose on glycine requirement of Acanthamoeba castellanii

Acanthamoeba castellanii grows in a minimal medium (AMLIV) containing only arginine, methionine, leucine, isoleucine, and valine as sole nitrogen sources, other than vitamins, when glucose is the carbon source. With acetate as the carbon source, glycine must be added to AMLIV. Doubling time in AMLIV varies according to the ratio of amino acids concentrations. Several combinations yield Td values of approximately 70 hr.

Inhibition of cell division in amoebae: the incorporation of tritiated precursors into Amoeba proteus after the injection of non-homologous cytoplasm

The injection of non-homologous cytoplasm into any strain of large free-living amoebae leads to a 60% inhibition of division amongst recipient cells. When the post-microsomal supernatant fraction of Amoeba discoides was injected into A. proteus, this inhibition of division was as high as 95%. The incorporation of tritiated precursors, either [3H]uridine or 3H-amino acids, into these inhibited amoebae was studied at various times after the injection of the inhibitory material using autoradiography. When cells were grown in [3H]uridine, autoradiographs indicated that RNA synthesis had ceased 2 days after the injection of non-homologous material. However, if [3H]uridine was injected into the inhibited cells, some synthesis of RNA could be detected up to 4 days after the injection of inhibitor. These results suggested that uptake of [3H]uridine was impaired and that one site of action of the inhibitory molecules was RNA synthesis for membrane components. Experiments with a variety of 3H-amino acids suggested that protein synthesis continued for at least 9 days after the injection of non-homologous cytoplasm, and that in these cells some informational RNA molecules were long-lived. There seemed to be accumulation of material containing [3H]lysine in the nuclei of control cells taken at random from cultures, and this was seen in the nuclei of inhibited cells 1 day after injection. However, 2 days after the injection of inhibitor, no accumulation of [3H]lysine-containing material was found in the nuclei.

In vitro effects of amphotericin B on growth and ultrastructure of the amoeboflagellates Naegleria gruberi and Naegleria fowleri

In vitro effects of the polyene antibiotic amphotericin B (AmB) on growth, viability, and ultrastructure of amoeboflagellates of the genus Naegleria were examined. The strains studied were the nonpathogenic Naegleria gruberi EG(B) and the Carter and TY strains of the pathogenic Naegleria fowleri. AmB was amoebicidal at all concentrations used (0.25, 0.50, and 1.0 mug/ml) when the drug was added to cultures in lag phase, as determined by viability testing, but was mainly inhibitory when added to log-phase cultures. The drug produced ultrastructural modifications at all concentrations (0.05 to 1.0 mug/ml). These changes included distortion of nuclear shape, increase in cytoplasmic membranes (both rough and smooth endoplasmic reticulum), decrease in number of food vacuoles, absence of pseudopod formation, mitochondrial abnormalities, increase in autophagic vacuoles, and blebbing of the plasma membrane. These alterations of amoebic ultrastructure became more pronounced with increased time in AmB and with increase in AmB concentration in the growth medium.

Effect of near ultraviolet and visible light on amoeba

The near ultraviolet and visible light (VL) impinging at an intensity of 2–5 × 10(2) J s-1 m-2 for 2–5 h kills the mitotic and the early S-phase (0- to 15-min-old) amoebae. At the mid- and late S-period only a fraction of cells are killed by VL and G2 phase cells are quite resistant. Amoebae of all cell cycle stages show a delay in the first mitotic division. DNA synthesis, as measured by [3H]thymidine incorporation, is depressed in the VL-exposed early-S amoebae. A concurrent but temporary inhibition in [3H]leucine incorporation also occurs in these cells. However, no significant change in [3H]uridine incorporation has been found. To localize the site of lethal damage, nuclear transplantation studies were undertaken between the control amoebae and the amoebae treated with VL. The nucleus of a VL-exposed early S-phase cell recovers when transplanted immediately after VL exposure into an enucleate G2 cytoplasm but dies if grafted into an enucleat S-phase cytoplasm. The therapeutic effect of the G2 cytoplasm, although at a lower level, is also evident even when the treated early S-phase nucleus is implanted 20 h later, but not after 48 h, into the G2 cytoplasm. The amoeba cytoplasm shows resistance to VL-irradiation, can accept a control nucleus from any cell cycle stage, and function normally. The G2 nucleus also remains apparently unaffected to VL exposure and can survive when it is transfered to the control cytoplasm of any cell-cycle phase. All these findings are discussed in the light of the possible existence of a repair system against VL-induced damage in the G2-phase amoeba.

The effect of thermal pollution on the distribution of Naegleria fowleri

The distribution in the environment of Naegleria fowleri, the causal agent of primary amoebic meningoencephalitis has been investigated in this study. N. fowleri was isolated only from a thermally polluted canal. These amoebaflagellates were not isolated from another thermally polluted canal in the neighbourhood indicating that, apart from high temperature, other factors are involved in the selective proliferation of N. fowleri. This species was absent in all other samples originating from two canals, a stream, two lakes, several reservoirs and slow sandfilters of a water supply service and also a water distribution network. Many other amoebae able to grow at 42 degrees C. were found in different places. Most of the N. fowleri strains isolated were not virulent for mice, although they showed all the characteristics of the pathogenic strains.

Experimental infections with pathogenic free-living amebae in laboratory primate hosts: I. (B) A study on susceptibility to Acanthamoeba culbertsoni

Susceptibility to A. culbertsoni was studied in 15 Old World monkeys by intranasal, intravenous, or intrathecal inoculation of trophozoites. No clinically detectable disease resulted from either intranasal or intravenous inoculation, but 4 of 7 monkeys inoculated intrathecally succumbed to acutely fatal meningoencephalitis. Virulence of the ameba varied with cultural age of the inoculum. Size of inoculum, passages through animal tissues, and host-immune competence were other factors of consideration in pathogenicity of the ameba.

Nuclear division in the ameboflagellate Adelphamoeba galeacystis

Nuclear division is synchronized cultures of the ameoboflagellate Adelphamoeba galecystis has been described. Division in this organism is typically promitotic. It occurs within an intact nuclear membrane and is characterized by the persistence of the nucleolus and its transformation into 2 polar masses. The nucleolus is stained with pyronin-Y by the methyl green pyronin-Y technic, and with Heidenhain's hematoxylin, but is unstained by the Feulgen reaction. The reaction with these stsins is removed after digestion of the nucleolus by ribonuclease. During mitosis the nucleolus undergoes an orderly series of vacuolizations before forming the polar masses. The chromatin is Feulgen positive, stains with methyl green by the methyl green pyronin-Y technic and undergoes a series of characteristic changes during the division process. Synchronizationof amebae grown on coverglasses was accomplished by transfer of cells from 30 to 38.5 C for a period of 100 min. A temporal sequence of nucleolar and chromatin participation in the nuclear division of this organism is suggested.

Experimental infections with pathogenic free-living amebae in laboratory primate hosts: I (A) A study on susceptibility to Naegleria fowleri

Studies were conducted on 27 Old World monkeys to determine their susceptibility to pathogenic strains (HB-1 and C-66) of Naegleria fowleri by intranasal, intravenous, or intrathecal inoculation of trophozoites. No clinically detectable disease resulted from either intranasal or intravenous inoculation, but 11 of 18 monkeys inoculated intrathecally succumed to acutely fatal meningoencephalitis, while the other 7 survived with no obvious permanent brain damage. Pathogenicity of N. fowleri appeared to be influenced by the strain virulence, growth phase, and cultural condition of the amebae, as well as age, immune competence, and other as yet unknown host factors.

DNA-dependent RNA polymerases from Acanthamoeba castellanii: properties and levels of activity during encystment

Three DNA-dependent RNA polymerases have been isolated and partially purified from trophozoites of Acanthamoeba castellanii. Separated by DEAE-Sephadex chromatography, they have been designated polymerases, I, IIa and IIB according to their alpha-amanitin sensitivity and kinetic properties. I is completely insensitive to alpha-amanitin. IIa and IIb are sensitive to low concentrations (0.1 mug/ml) of alpha-amanitin; however, in order to achieve 100% inhibition much higher concentrations (130 mug/ml) are needed. Both I and II (a or b) have rather broad ionic strength optima (0.06--0.10 M (NH4)2SO4). All three prefer denatured over native DNA (I, 4:1; II, 2:1). Polymerase I utilizes magnesium better than manganese as divalent cation whereas II prefers manganese. When Acanthamoeba is transferred to a medium lacking nutrients, the cells undergo a synchronous differentiation resulting in cyst formation. In general agreement with the decrease in the rate of synthesis of its product (rRNA), the amount of polymerase I decreases relative to the amanitin sensitive polymerase(s). However, the absolute amount of polymerase I does not change. Rather, the levels of the amanitin sensitive enzymes increase during the first 10 h of encystment. Since the overall RNA synthesis rate decreases, these results suggest that the transcription rate is not controlled by specific enzyme levels alone.

Cultivation of Acanthamoeba castellanii, Neff Strain, at high hydrostatic pressures

Log-phase cultures of Acanthamoeba castellanii, Neff strain, have been maintained at elevated hydrostatic pressures over periods of several days and the population has been recounted at the end of the experimental period. A pressure of 2,000 psi (136 atm) depressed growth of the population, but was quickly reversed on release. A pressure of 4,000 psi (272 atm) severly depressed population growth, and any increase was slight and short-lasting at 5,000 psi (340 atm). Growth of the population was resumed only after an interval of 1 or more days after release.

Biologic and serologic characterization of the 161A strain of Naegleria fowleri

The 161A strain of Naegleria isolated from the nasal swab of a boy (9) was grown axenically in Nelson's medium. When 10,000 amoebae from the axenic medium were inoculated onto each monkey kidney cell (Vero) culture, characteristic cytopathic effects (CPE) were noticed in 4 to 5 days. The CPE consisted of granulation of the host cell cytoplasm, cell shrinkage, nuclear pycnosis, and discontinuity of cell sheet. When 10,000 amoebae were instilled intranasally into a group of ten 2- to 3-week-old mice, 8 of the 10 mice exhibited characteristic symptoms of primary amoebic meningoencephalitis and died within 10 to 12 days. Histopathology of the brain revealed necrotic tissue and an acute inflammatory reaction in the superficial regions of the brain. In the gel diffusion and immunoelectrophoresis tests the sonically disrupted antigens of 161A amoebae reacted extensively with the hyper-immune sera against 3 strains (CA, CJ, HB-1) of pathogenic N. fowleri and produced patterns very similar to those produced by the homologous systems. Further, anti-HB-1 serum absorbed with the 161A antigens failed to react with the antigens of HB-1, CA, CJ, and 161A strains thus indicating antigenic identity of 161A strain with N. fowleri. In view of these observations it was concluded that the strain 161A is pathogenic and should be reclassified as N. fowleri.