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PubMed1977

Structural and biochemical aspects of cell motility in amebas of Dictyostelium discoideum.

Amebas of Dictyostelium discoideum contain both microfilaments and microtubules. Microfilaments, found primarily in a cortical filament network, aggregate into bundles when glycerinated cells contract in response to Mg-ATP. These cortical filaments bind heavy meromyosin. Microtubules are sparse in amebas before aggregation. Colchicine, griseofulvin, or cold treatments do not affect cell motility or cell shape. Saltatory movement of cytoplasmic particles is inhibited by these treatments and the particles subsequently accumulate in the posterior of the cell. Cell motility rate changes as Dicytostelium amebas go through different stages of the life cycle. Quantitation of cellular actin by sodium dodecyl sulfate-polyacrylamide gel electrophoresis shows that the quantity of cellular actin changes during the life cycle. These changes in actin are directly correlated with changes in motility rate. Addition of cyclic AMP to Dictyostelium cultures at the end of the feeding stage prevents a decline in motility rate during the preaggregation stage. Cyclic AMP also modifies the change in actin content of the cells during preaggregation.

Actins↗
PubMed1992

Culture isolation of Acanthamoeba species and leptomyxid amebas from patients with amebic meningoencephalitis, including two patients with AIDS.

Acanthamoeba species and leptomyxid organisms are free-living amebas that cause meningoencephalitis, primarily in immunocompromised patients. We report the isolation and culture of Acanthamoeba species and leptomyxid amebas from four patients with fatal amebic meningoencephalitis. Acanthamoeba species were cultured from brain abscess specimens from three immunocompromised patients (including two patients with AIDS). In the case of the fourth patient, who had no identifiable immunodeficiency, leptomyxid amebas were cultured from a specimen from a subcutaneous nodule and were identified in amebic granulomas in brain tissue by the indirect immunofluorescence test. Persons with advanced infection due to the human immunodeficiency virus may be at increased risk for amebic meningoencephalitis, but the diagnosis should be considered in the differential diagnosis of any immunocompromised patient with cerebral abscesses.

AIDS-Related Opportunistic Infections↗
PubMed1978

The occurrence of amphizoic Amebae in domestic animals.

Random examination of domestic animals revealed the frequent presence of free-living amebae in their bodies. In diseased or dead cows, dogs, pigs, rabbits, pigeons, and turkeys 15 strains of amebae were found, belonging to the genera Acanthamoeba (A. polyphaga), Hartmannella (H. vermiformis), and Vahlkampfia (V. avara, V. enterica, V. inornata). They were usually accompanied by other infectious agents in different parts of the host bodies. Pathogenicity of 3 isolates could not be demonstrated by inoculation of laboratory animals. Some features of the isolates differed from those previously known for members of these genera. These strains may be considered amphizoic amebae according to Page (1974).

Amebiasis↗
PubMedDate not supplied

Efficacy of novel antimicrobials against clinical isolates of opportunistic amebas.

We examined the effects of the macrolide antimicrobial agent azithromycin and phenothiazine compounds against clinical isolates of Acanthamoeba spp. and Balamuthia mandrillaris, opportunistic pathogens of human beings and other animals. Acanthamoeba growth was inhibited in vitro at 1, 5, and 10 micrograms/ml of azithromycin, but not the macrolides, erythromycin, and clarithromycin. In experiments attempting to simulate in vivo conditions, azithromycin protected monolayers of rat glioma cells from destruction by Acanthamoeba at a concentration of 0.1 microgram/ml, and delayed destruction at concentrations of 0.001 and 0.01 microgram/ml. We concluded that the minimal inhibitory concentration of azithromycin was 0.1 microgram/ml. Our results, however, suggested that the drug was amebastatic but not amebicidal, since ameba growth eventually resumed after drug removal. The phenothiazines (chlorpromazine, chlorprothixene, and triflupromazine) inhibited Acanthamoeba growth by 70-90% at 5 and 10 micrograms/ml, but some of these compounds were toxic for rat glioma cells at 10 micrograms/ml. Azithromycin was not very effective against B. mandrillaris in an in vitro setting, but was amebastatic in tissue culture monolayers at concentrations of 0.1 microgram/ml and higher. Balamuthia amebas showed in vitro sensitivity to phenothiazines. Ameba growth was inhibited 30-45% at 5 micrograms/ml in vitro, but completely at 5 micrograms/ml in the rat glioma model. In spite of their potential as antiamebic drugs in Balamuthia infections, toxicity of phenothiazines limits their use in clinical settings.

Acanthamoeba↗
PubMed1977

The nature of a cytopathogenic material present in amebae of the genus Naegleria.

The Naegleria ameba cytopathogenic material (NACM) obtained from free-living and/or pathogenic amebae has been partially isolated and characterized. The evidence indicates that the material is a protein or has a protein component, and is in the estimated molecular weight range of 50,000 daltons. The partially isolated NACM, like its counterpart in the amebic lysates, is capable of sustaining itself in tissue cultures at a temperature which otherwise would inactivate it, and in serial passages through multiple dilutions. No distinctions between the NACMs from amebae of different Naegleria species or strains have been found in the biological response to the various treatments studied.

Amoeba↗
PubMed1991

Amebic meningoencephalitis in a patient with AIDS caused by a newly recognized opportunistic pathogen. Leptomyxid ameba.

A fatal case of meningoencephalitis due to a leptomyxid ameba in a patient with the acquired immunodeficiency syndrome is presented. This opportunistic organism has not been previously recognized as a human pathogen. A 36-year-old male intravenous drug abuser died after an 18-day hospital course heralded by fever and headache and followed by nuchal rigidity and hemiparesis. Computed tomography of the head showed multiple hypodense lesions. Neuropathologic examination showed that in addition to human immunodeficiency virus encephalomyelitis, there was multifocal meningoencephalitis with trophozoites and cysts morphologically indistinguishable from those of Acanthamoeba. These organisms were also found in the kidneys and adrenal glands. By immunofluorescence, the parasites showed antigenic identity with a free-living leptomyxid ameba and failed to react with any of a spectrum of antiacanthamoeba antisera. This emphasizes the importance of immunofluorescence identification of morphologically indistinguishable ameba species.

Acquired Immunodeficiency Syndrome↗
PubMed1989

When should we look for amebae in patients with inflammatory bowel disease?

Amebic colitis can mimick Crohn's disease of the colon and ulcerative colitis. Inflammatory bowel disease (IBD) patients can also be carriers of amebae. Since steroids can provoke amebic activity and even cause a fulminating colitis, it is necessary to determine that amebae do or do not exist. Furthermore, amebae can be easily eliminated by drug therapy but it is hard to eradicate IBD. Despite the above, diagnostic modalities for IBD are as effective as those for amebiasis, particularly for Crohn's disease with ileal involvement. Problems in differential diagnosis arise with IBD grossly limited to the colon. In these cases, false negative stool studies are increased by diarrhea and preparation for examinations, and both stool studies and serologies are compromised by steroids. If the clinical course of IBD is downhill, the clinician is justified in starting steroids even if evaluation for amebiasis incomplete. If, however, the index of suspicion is high, concomitant treatment with Metronidazole would be reasonable.

Diagnosis, Differential↗
PubMed1993

Free-living amebas of the genera Acanthamoeba and Naegleria: an overview and basic microbiologic correlates.

Free-living amebas of the genera Acanthamoeba and Naegleria are allied in basic cell biology, ecology, and human disease-producing potential. However, several enigmas surrounding these amebas need further intellectual and scientific scrutiny. For instance, a clearer differentiation is needed of factors delineating pathogenic species--those most frequently associated with human infections--from nonpathogenic species. Further, have the pathogenic species bridged the gap in a step-wise fashion between their habitat and the human host to express their disease-producing potential? Second, what attributes of amebas account for the spectrum of disease caused by Acanthamoeba and Naegleria? In the brain, Naegleria is highly destructive of tissue in the course of a rapidly evolving, hemorrhagic primary meningoencephalitis in normal individuals. Central nervous system invasion by Acanthamoeba, however, occurs only in compromised hosts, and is a more slowly evolving subacute to chronic encephalitis. Further, the epidemiology of the infections are disparate. Naegleria is acquired from exposure to contaminated fresh water; this epidemiologic link is absent in Acanthamoeba meningoencephalitis. Naegleria invades the central nervous system via the olfactory nerve; Acanthamoeba is deposited in the central nervous system via hematogenous spread from a pulmonary or cutaneous focus. Additionally, Naegleria is apparently restricted to the brain; Acanthamoeba is not so bridled, and invades more sites in the human body. Finally, Acanthamoeba are beginning to appear opportunistically more frequently in patients infected with the human immunodeficiency virus. To avoid the same lack of effective therapeutics we still face in treating cryptosporidium infections in these patients, more emphasis must be placed on clinical trials dealing with the management of Acanthamoeba infections in patients with AIDS.

Acanthamoeba↗
PubMed1977

Isolation and experimental infection of free-living amebae in freshwater fishes.

Twenty-three species of fish from nine southeastern states were screened for the presence of small, free-living amebae. Organs from 11 species of fish contained amebae of the genera Acanthamoeba, Naegleria, and Vahlkampfia. Three strains of Acanthamoeba were injected into fish to determine infectivity and pathogenicity of the amebae. Strains used were an A. polyphaga MC-1 isolated from the spleen of a bass, the pathogenic A-5 strain of A. culbertsoni, and the pathogenic Lilly A-1 strain of A. culbertsoni. The MC-1 strain established systemic infections in many organs of the test fish. The 2 strains of A. culbertsoni did not produce any infection in fish under the laboratory conditions.

Amebiasis↗
PubMed1996

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↗
PubMed2006

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

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

Acanthamoeba↗
PubMed1992

Entamoeba histolytica: is conversion of "nonpathogenic" amebae to the "pathogenic" form a real phenomenon?

Entamoeba histolytica isolates have been shown to fall into two groups based on isoenzyme analysis. These groupings ("pathogenic" and "nonpathogenic") correlate well with the clinical course of the infection. A controversy exists over whether isoenzyme patterns are stable or whether under certain circumstances an isolate can convert from one form to the other. Resolution of this uncertainty is of importance since the nonpathogenic pattern has never been observed in amebae isolated from cases of active disease. This implies that, if the patterns are stable, carriers of amebae with this nonpathogenic pattern may never develop invasive disease. Although we set out to study isoenzyme conversion, we have been unable to replicate the two published accounts of this phenomenon. We have examined all of the variables proposed to be involved in the triggering of conversion, both individually and in combination. In none of the experiments was an alteration in the isoenzyme pattern observed. We now believe that isoenzyme patterns are stable and that all available evidence, other than the reported conversions, points to pathogenic and nonpathogenic E. histolytica being distinct species.

Animals↗
PubMed2004

Amebae and ciliated protozoa as causal agents of waterborne zoonotic disease.

The roles free-living amebae and the parasitic protozoa Entamoeba histolytica and Balantidium coli play as agents of waterborne zoonotic diseases are examined. The free-living soil and water amebae Naegleria fowleri, Acanthamoeba spp., and Balamuthia mandrillaris are recognized etiologic agents of mostly fatal amebic encephalitides in humans and other animals, with immunocompromised and immunocompetent hosts among the victims. Acanthamoeba spp. are also agents of amebic keratitis. Infection is through the respiratory tract, breaks in the skin, or by uptake of water into the nostrils, with spread to the central nervous system. E. histolytica and B. coli are parasitic protozoa that cause amebic dysentery and balantidiasis, respectively. Both intestinal infections are spread via a fecal-oral route, with cysts as the infective stage. Although the amebic encephalitides can be acquired by contact with water, they are not, strictly speaking, waterborne diseases and are not transmitted to humans from animals. Non-human primates and swine are reservoirs for E. histolytica and B. coli, and the diseases they cause are acquired from cysts, usually in sewage-contaminated water. Amebic dysentery and balantidiasis are examples of zoonotic waterborne infections, though human-to-human transmission can occur. The epidemiology of the diseases is examined, as are diagnostic procedures, anti-microbial interventions, and the influence of globalization, climate change, and technological advances on their spread.

Acanthamoeba↗
PubMed2002

Calcium-dependent protection from complement lysis in Naegleria fowleri amebae.

Pathogenic Naegleria fowleri amebae are resistant to the lytic effects of serum complement. The presence of surface glycoproteins or removal of the membrane attack complex (MAC) of complement from the cell surface by vesiculation serve to protect the amebae from complement lysis. The specific mediators important in stimulating complement resistance are not defined. These studies were undertaken to examine the effect of Ca(2+) ions in initiating complement resistance of N. fowleri in contrast to non-pathogenic complement-sensitive N. gruberi. Chelation of extracellular calcium with ethylene glycol tetraacetic acid (EGTA) or chelation of intracellular calcium with 1,2-bis-(O-Aminophenoxy) ethane-N,N,N,N tetraacetic acid tetra (acetoxymethyl) ester (BAPTA-AM) increased complement lysis of N. fowleri. Chelation of calcium ions did not affect complement sensitivity of N. gruberi. Increased lysis of ionomycin-treated N. fowleri was detected after exposure to serum complement, suggesting that a threshold level of Ca(2+) mediates complement resistance before survival mechanisms are overwhelmed and lysis occurs. A differential influx of Ca(2+) ions occurred in fura-2 labeled N. fowleri after deposition of complement component C9 to form the MAC complex on the cell surface in comparison to N. gruberi. These studies suggest that Ca(2+) ions influence complement resistance in N. fowleri but do not play a role in altering the sensitivity of N. gruberi to complement.

Animals↗
PubMed1988

Interaction between pathogenic amebas and fibronectin: substrate degradation and changes in cytoskeleton organization.

Invasion of human tissues by the parasitic protozoan Entamoeba histolytica is a multistep process involving, as a first step, the recognition of surface molecules on target tissues by the amebas or trophozoites. This initial contact is followed by the release of proteolytic and other activities that lyse target cells and degrade the extracellular matrix. In other parasitic diseases, as well as in certain cancers, the interaction of invasive organisms or cells with fibronectin (FN) through specific receptors has been shown to be the initial step in target cell recognition. Interaction with FN triggers the release of proteolytic activities necessary for the effector cell migration and invasion. Here, we describe the specific interaction of Entamoeba histolytica trophozoites with FN, and identify a 37-kD membrane peptide as the putative receptor for FN. The interaction between the parasite and FN leads to a response reaction that includes the secretion of proteases that degrade the bound FN and the rearrangement of amebic actin into "adhesion plates" at sites of contact with FN-coated surfaces. The kinetics of the interaction was determined by measuring the binding of soluble 125I-FN to the trophozoites and visualization of the bound protein using specific antibodies. Degradation of FN was measured by gel electrophoresis and the release of radioactivity into the incubation medium. Focal degradation of FN was visualized as black spots under the trophozoites at contact sites with fluorescent FN. We conclude that the interaction of E. histolytica with FN occurs through a specific surface receptor. The interaction promotes amebic cytoskeleton changes and release of proteases from the parasite. The binding and degradation of extracellular matrix components may facilitate the migration and penetration of amebas into tissues, causing the lesions seen in human hosts.

Actins↗
PubMed1962

An electron microscopic study of pinocytosis in ameba. II. The cytoplasmic uptake phase.

This report is devoted principally to a consideration of the fate of the pinocytotic vacuole and its content in the ameba Pelomyxa carolinensis (Chaos chaos). High resolution micrographs of the plasmalemma have shown it to consist of three layers, i.e., an outermost filamentiferous zone, a middle homogeneous zone, and an inner zone which appears to be a unit membrane. The three zones can be identified in the membranes lining the pinoyctotic tunnels and vacuoles of amebas fixed shortly after pinocytosis occurred. The first apparent change in the pinocytotic vacuole is an increase in the surface-to-volume ratio which occurs during the 1st hour of its existence. Within 24 hours the marker substance commonly collects in defecation vacuoles which can be identified by the profiles of bacteria usually found in the lumen. Occasionally, however, thorotrast can be seen in the lumen of the contractile vacuole. The thorotrast appears to enter the two excretory organelles by the coalescence of vesicular fragments of the pinocytotic vacuoles with the limiting membranes of the excretory organelles.

Amoeba↗
PubMed1965

A study of phagocytosis in the ameba Chaos chaos.

The process of phagocytosis was investigated by observing the interactions between the ameba Chaos chaos and its prey (Paramecium aurelia), by studying food cup formation in the living cell, and by studying the fine structure of the newly formed cup using electron microscopy of serial sections. The cytoplasm surrounding the food cup was found to contain structures not seen elsewhere in the ameba. The results are discussed in relation to the mechanisms which operate during food cup formation.

Eukaryota↗
PubMed1967

The ameba-to-flagellate transformation in Tetramitus rostratus. II. Microtubular morphogenesis.

Tetramitus exhibits independent ameboid and flagellate stages of remarkable morphological dichotomy. Transformation of the ameba involves the formation of four kinetosomes and their flagella. The arrangement of these kinetosomes and associated whorls of microtubules extending under the pellicle establishes the asymmetric flagellate form. While no recognizable kinetosomal precursors have been seen in amebae, and there is no suggestion of self-replication in dividing flagellates, developmental stages of kinetosomes have been identified. These are occasionally seen in association with the nucleus or with dense bodies which lie either inside of or close to the proximal end of the prokinetosome. Outgrowth of flagella involves formation of an axoneme and a membrane. From the distal tip of the kinetosome microtubules grow into a short bud, which soon forms an expanded balloon containing a reticulum of finely beaded filaments. The free ends of the microtubules appear unraveled; they are seen first as single elements, then as doublets, and finally are arranged into a cylinder. Growth in length is accompanied by a reduction in the diameter of the balloon. The concept that the formation of the kinetic apparatus might involve a nuclear contribution, followed by a spontaneous assembly of microtubules, is suggested.

Animals↗